I can't figure out how to open the printer to change the black ink cartridge

It won't recognise the black cartridge in the printer and may even throw an error code. Use the black and white option setting for printing.

Here is the download for your instructions:

http://gdlp01.c-wss.com/gds/0/0300002510/01/MP990_GS_EN-US_V1.pdf

A note about PDF files: If you cannot view a given file, you need to first install Adobe Reader. You can get the free download here:
http://get.adobe.com/reader/

Once you have the download opened, follow the instructions under the "Hardware Setup" heading.
It does not appear that the ink cartridges are at the back of the printer in the illustrations.

Supported HP Inkjet cartridge part numbers The HP Officejet 4100 all-in-one series products use the ink cartridges listed in the table below. HP Inkjet cartridges HP 56 black cartridge (19 ml) HP 57 tri-color cartridge (17 ml) HP 28 tri-color cartridge (8 ml) Replacing the ink cartridgesThe power must be turned ON to the all-in-one or the print carriage will not move to the right.

1. Locate and open the print cartridge access door on the right side of the all-in-one. The print cartridge carriage will move to the right for access. Figure 1: Opening the HP Officejet 4100 series
2. Press down gently on the top of the old ink cartridge to release it from the print carriage. Figure 2: Removing an ink cartridge
3. Remove the new print cartridge from its packaging and remove the protective tape from the cartridge as shown in Figure 3. Do not touch the gold-colored contacts. Figure 3: Removing the cartridge tape
4. Holding the ink cartridge with the printed label up, slide the cartridges one at a time into the print carriage and press them into position as shown in Figure 4. If the cartridge does not snap easily into position, it is not aligned correctly. Remove the cartridge and reposition it. Do not try to force the cartridge into position. The black ink cartridge (HP #56) goes on the right side and the color cartridge (HP #57 or HP #28) goes on the left side. Close the ink cartridge access door when the ink cartridge has been installed. Figure 4: Installing the ink cartridges
5. A message will appear on the front panel requesting that the ink cartridges be aligned. Follow the steps below to align the ink cartridges:
   1. Press Enter on the all-in-one front panel to start the ink cartridge alignment process.
   2. After the Alignment page prints, place the page into the ADF upside down and with the printed side down as is shown in Figure 5.
   3. Press Enter. The all-in-one will scan the alignment page and finish aligning the cartridges.
   Figure 5: Aligning the ink cartridges

Correcting error messages that appear after changing a cartridgeAfter inserting the cartridge, the Check Print Cartridge light flashes or one of the following messages appears on the computer monitor:

• Check the black (or color) cartridge
• Replace the black (or color) cartridge
• The wrong black (or color) cartridge is installed

These messages indicate that the ink cartridge is not making good electrical contact, is bad, or is the wrong cartridge. Complete the following steps to diagnose and correct the condition:

1. Open the front of the unit to access the print cartridges (as shown in Figure 1).
2. Remove the ink cartridge and inspect it.
3. Verify that it is the correct part number and if it is, reinsert it.
4. Close the lid to see if the problem is corrected.
5. If the message is still displayed after a few seconds, remove the ink cartridge again.
6. Unplug the power cord from the back of the unit.
7. Clean the electrical contacts on the ink cartridge with a soft clean cloth slightly dampened (not wet) with clean water. (See Figure 6) Each contact is very small and shaped like a rounded square. Figure 6: Cleaning the cartridge contacts
8. Allow the ink cartridge to dry for a few minutes before reinserting the cartridge(s) and turning on the printer.
9. If the problem remains, replace the ink cartridge.
10. If the problem still exists after trying all of the steps above, the unit may need to be serviced. Contact HP for further troubleshooting or to arrange to have the unit serviced.

Make sure what ur using isn't a refilled cartridge and if it is check the expiration date, if nothing is wrong then you need to get urself a new printer or an upgrade so call up hp at 1800-474-6836 and get help of them,they'll guide you to a new /upgrade printer.
it's not a nice way of saying it but someone has to give you the bad news

The following text copied from HP website to tackle this problem. Follow the instructions below to install the print cartridges. NOTE: If you are installing ink cartridges in the unit for the first time, be sure to use only the print cartridges that came with the unit. The ink in these cartridges is specially formulated to mix with the ink in the print head assembly at first-time setup. Installing the print cartridges

1. Verify that the unit is on.
2. Open the ink cartridge door. Figure 1: Opening the ink cartridge door
3. Squeeze the gray tab below an ink cartridge slot to release the gray latch and then lift the latch. Figure 2: Lifting the latch 1 - Ink cartridge latch for the black ink cartridge 2 - Ink cartridge latches for the color ink cartridges NOTE: The ink cartridge areas are color-coded for easy reference. From left to right, the ink cartridges are black, yellow, light cyan, cyan, light magenta, and magenta.
4. Remove the new ink cartridge from its packaging.
5. Hold the ink cartridge by the handle and then slide the ink cartridge into the empty slot. NOTE: Make sure that the ink cartridge is inserted into the slot that has the same shaped icon and color as the ink cartridge. The copper-colored contacts should be facing the printer as the ink cartridge is inserted. Figure 3: Inserting an ink cartridge
6. Press down on the gray latch until it clicks into place. Figure 4: Closing the gray latch
7. Repeat steps 3 through 6 for each ink cartridge that needs to be replaced. NOTE: All six cartridges must be installed. The printer will not work if an ink cartridge is missing.
8. Close the ink cartridge door. Figure 5: Closing the ink cartridge door

Have a Good Day

http://crm01.konicaminoltaeurope.com/openmind/technic/engineer/qmspubkb.nsf/0/70744652a954e650c1256f820078e0a2/$FILE/MC24x0-Replace%20Toner%20Cartridge.pdf
Goto the above link and it shows the PDF doc. for changing the cartrides.

Solution Replace the indicated ink cartridge(s), or press OK on the control panel to continue. HP recommends the use of genuine HP ink cartridges. Genuine HP ink cartridges are designed and tested with HP printers to help produce great results, time after time.
NOTE: HP cannot guarantee the quality or reliability of non-HP ink. Printer service or repairs required as a result of printer failure or damage due to the use of non-HP ink will not be covered under warranty. Follow these steps to replace the depleted HP ink cartridge(s). Step one: Replace the indicated cartridge(s)

1. Make sure the HP All-in-One is turned on.
   NOTE: The Attention light blinks when the product is turned on.
2. Open the access door by lifting from the front center of the HP All-in-One, until the door locks into place. Figure 1: Opening the access door
3. Squeeze the bottom of the latch below the ink cartridge to replace, and then lift the latch.
   • To replace the black ink cartridge, lift the latch on the far left.
   • To replace one of the five color ink cartridges, such as yellow, light cyan (blue), cyan, light magenta (pink), or magenta, lift the appropriate latch in the center area.
   Figure 2: Lifting the latch 1 - Ink cartridge latch for the black ink cartridge 2 - Ink cartridge latches for the color ink cartridges
4. Pull the ink cartridge towards you out of its slot to remove it. Figure 3: Removing the ink cartridge
5. Remove the new ink cartridge from its packaging.
6. Holding the new ink cartridge by the handle, push the ink cartridge into the empty slot. Match the color and pattern of the ink cartridge to the color and pattern on the print carriage. Figure 4: Inserting the new cartridge
7. Close the latch, and make sure it is secure.
8. Close the access door. Figure 5: Closing the access door

Step two: Align the new ink cartridge(s)

1. Make sure paper is loaded in the input tray, and then press the OK button. The HP All-in-One prints the alignment page, aligns the printhead, and initializes the ink cartridges. This takes approximately 5 minutes. CAUTION: Do not disconnect or turn off the HP All-in-One during this time. You may hear the HP All-in-One making noises.
2. Check the display for status, and then press the OK button. Recycle or discard the alignment page.

Cause The original HP ink in the indicated ink cartridge(s) has been depleted.

maybe your ink cartridge is damaged. Try to change your ink cartridge (black). Or your printer has reach the maximum capacity of pritning.. ^^

When you removed the paper it's possible your damaged it and that's why the message is not going away. Did you try to put the cartridge back in to make sure it had not come out of position and just remove the power cord for a minute then plugging it back it.

Here are the steps to make sure you properly change the cartridges and the heads...

Install the ink cartridges and printheads Step one: Install the ink cartridges All four ink cartridges must be correctly installed for the HP All-in-One to work. Follow the steps below to Install cartridges:

1. Open the ink cartridge cover.
2. Remove each ink cartridge from its package.
3. Align each ink cartridge with its color-coded slot and then insert the ink cartridge into the slot. To ensure proper contact, press down firmly on the cartridges until they snap into place.
4. Close the ink cartridge cover.

Figure 1: Installing cartridges 1 - Open the ink cartridge cover. 2 - Remove the ink cartridges from the packages. 3 - Install the ink cartridges. 4 - Close the ink cartridge cover. Step two: Install the printheads Follow the steps below to install the printheads.

1. Open the top cover of the printer. Figure 2: Open the top cover
2. If the carriage does not move to the left automatically, press and hold the Resume button ( ) for three seconds. Wait for the carriage to stop moving.
3. Remove the cardboard cover from the printhead carriage. Figure 3: Remove the cardboard cover
4. Lift the printhead latch. Figure 4: Lift the printhead latch
5. Before installing a printhead, shake the printhead up and down at least six times while the printhead is still in its packaging. Figure 5: Shake the printhead while it is still in its packaging
6. Remove the new printhead from its package, and then remove its orange protective caps. CAUTION: Do not shake printheads after the caps are removed. Figure 6: Remove the printhead from its packaging, then remove the orange caps from the printhead
7. Insert the printhead into its color-coded slot. The label on the printhead must match the label on the printhead latch. Press down firmly on the printhead to ensure proper contact. Figure 7: Insert the printheads in the correct color-coded slots
8. Pull the printhead latch all the way forward, and then press down to ensure that the latch is properly engaged. You might have to apply some pressure to engage the latch. Figure 8: Close the latch
9. Close the top cover. Figure 9: Close the top cover

Step three: Align the print heads Whenever you insert or replace a printhead, the printer automatically aligns the printheads to ensure the best print quality. If the printer does not print the alignment page automatically, start the alignment process manually. To start the alignment process manually:

1. Press the Setup button on the control panel Setup and the number 6 on the keypad or scroll to Tools .
2. Press 4 on the keypad or scroll to Align Printer . The alignment process starts.

Follow the steps below to remove and replace the empty ink cartridge.

1. Turn the printer on.
2. Open the ink cartridge door. Figure 1: Opening the ink cartridge door
3. Squeeze the gray tab below an ink cartridge slot to release the gray latch and then lift the latch. Figure 2: Lifting the latch 1 - Ink cartridge latch for the black ink cartridge 2 - Ink cartridge latches for the color ink cartridges
   NOTE: Theink cartridge areas are color-coded for easy reference. From left toright, the ink cartridges are black, yellow, light cyan, cyan, lightmagenta, and magenta.
4. Pull the ink cartridge toward you out of it's slot to remove it. Figure 3: Removing an ink cartridge
5. Remove the new ink cartridge from the packaging.
6. Hold the ink cartridge by the handle and then slide the ink cartridge into the empty slot.
   NOTE: Makesure that the ink cartridge is inserted into the slot that has the sameshaped icon and color as the ink cartridge. The copper-colored contactsshould be facing the printer as the ink cartridge is inserted. Figure 4: Inserting an ink cartridge
7. Press down on the gray latch until it clicks into place. Figure 5: Closing the gray latch
8. Repeat steps 3 through 7 for each ink cartridge that needs to be replaced.
   NOTE: All six cartridges must be installed. The printer will not work if an ink cartridge is missing.
9. Close the ink cartridge door.

after Doing this all Follow the next step :-

Please Try This, I am sure it is going to workout.


Resetting the All-in-One
Press the On () button to turn off the unit.

• Disconnect the power cord from the back of the unit.
• Connect the power cord to the back of the unit.
• Press the On () button to turn on the unit.

Supported HP ink cartridge part numbers The HP PSC 2100, 2170, and 2200 all-in-one series products use the ink cartridges listed in the table below. The HP 58 tri-color photo ink cartridge replaces the black ink cartridge for six-ink photo printing. Ink cartridges Part number HP 56 black ink cartridge (19 ml) C6656A HP 57 tri-color ink cartridge (17 ml) C6657A HP 58 tri-color photo cartridge* (17 ml) C6658A HP 27 low capacity black ink cartridge (10 ml) C8727A HP 28 low capacity tri-color ink cartridge (8 ml) C8728A * Replaces the black ink cartridge for six ink photo printing and includes cartridge holder. Replacing the ink cartridges The power must be turned ON to the all-in-one or the print carriage will not come to the center.

1. Locate and raise the print cartridge access door on the front of the unit, just above the output tray. The print cartridge carriage will move into the middle of the access area. Figure 1: Raising the front access door and the ink cartridge latches
2. Press down lightly on the top of the ink cartridge latch of the ink cartridge to be replaced and then pull the lower section of the latch toward you to unlatch the ink cartridge.
3. Grasping the sides of the ink cartridge, pull the cartridge toward you to remove it as shown in Figure 2. Figure 2: Removing the cartridge after raising the latch
4. Remove the replacement cartridge from its packaging, and touching only the black plastic, gently remove any tape covering the nozzles. Do not touch the gold-colored contacts. Figure 3: Removing the protective tape
5. Holding the ink cartridge with the printed label up, slide the cartridges one at a time into the print carriage as shown in Figure 4. The black ink cartridge (HP 56 or HP 27) goes on the right side (with the gray latch) and the tri-color cartridge (HP 57 or HP 28) goes on the left side (with the blue latch). If the optional photo cartridge (HP 58) is installed for six-ink photo printing, it is installed in place of the black ink cartridge. Figure 4: Inserting the cartridge
6. Place your hand on the latch as shown in Figure 5, with the thumb pulling the end of the latch toward you. While holding the end of the latch out, press down on the top of the latch until it stops and then release the lower portion of the latch with your thumb so that it catches under the tabs. Do not force the latches into place or damage to the unit might occur. Close the all-in-one after latching the ink cartridges in place. Figure 5: Latching the ink cartridges in place
7. Close the print cartridge access door.
8. A message will appear in the front panel display requesting that the ink cartridges be aligned. Press ENTER on the front panel to start the cartridge alignment. Two pages will print. Following the instructions printed on the second page, place the first page on the scanner glass in the lower-right corner and then press ENTER to finish aligning the cartridges. Remove the page from the scanner glass when complete.

Storing the option photo printing cartridge while not in use The optional photo print cartridge (HP 58) that may be purchased separately for six-ink photo printing includes an ink cartridge protector. The protector is designed to keep the photo cartridge from drying out when it is not in use and for holding and protecting the black cartridge when the photo cartridge is in use.

• To insert a cartridge into the protector, slide it into the protector at a slight angle until it snaps in place.
• To remove a cartridge from the protector, push down and back on the top of the protector to release the cartridge and then slide the cartridge out of the protector.

Figure 6: Inserting and removing ink cartridges from the ink cartridge protector Fixing error messages that appear after changing a cartridge After inserting the cartridge, one of the following messages appears:

• Check the black (or color) cartridge
• Replace the black (or color) cartridge
• The wrong black (or color) cartridge is installed

These messages indicate that the ink cartridge is not making good electrical contact, is bad, or is the wrong cartridge. Complete the following steps to diagnose and correct the condition:

1. Open the front of the unit to access the print cartridges (as shown in Figure 1).
2. Remove the ink cartridge indicated in the message and inspect it.
3. Verify that it is the correct part number and if it is, reinsert it.
4. Close the lid to see if the problem is corrected.
5. If the message is still displayed after a few seconds, remove the ink cartridge again.
6. Unplug the power cord from the back of the unit.
7. Clean the electrical contacts on the ink cartridge with a soft clean cloth, slightly dampened (not wet) with clean water. Each contact is very small and shaped like a rounded square. Figure 7: Cleaning the cartridge contacts
8. Inside the HP all-in-one product, clean the contacts in the print carriage (the cartridge holder) with a clean cotton swab slightly dampened with clean water. Allow them to dry for five minutes before reinserting the cartridge(s) and turning on the printer. Figure 8: Contacts to be cleaned
9. If the problem remains, replace the ink cartridge.
10. If the problem still exists after trying all of the steps above, contact HP for assistance.