Since I have changed the cartridge, Whatever I try there is a message displayed :"cover open".

raise the cover and see if u can see a switch of some kind puss it down and see if it will print or restart ur computer and see what happens

Change the toner cartridge , i have many units phaser3200 and this is one of the problem , but only if the toner cartridge is very old and many time refilled , if not , change the Laser unit .

1. Remove a misfed document if the copier displays a message reading "Document Jam." Lift up the document feeder cover and turn the roller to remove an Exit Misfed document. Lower the document feeder back into place and feed the document through again. If the document is jammed on the Input side, open the cover and gently pull the misfed document to the right and out of the feeder.
   
2. Pull out the paper tray and lift the tray to release it from the copier if the copier displays a message reading "Paper Jam O." Remove the jammed document, and open and close the side panel of the copier to clear the error message.
   
3. Unplug the power cord and plug it back in again if the copier displays a message reading "Fuser Error, Open Heat Error, Heating Error and Overheat." If the problem persists, call for a service.
   
4. Remove the toner cartridge and shake it from side to side if the copier displays a message reading "No Developer Cartridge." If this does not do the trick, you may need to replace the cartridge. Pull the release latch to open the side cover, and open the front cover. Twist the cartridge locking-lever upwards and remove the toner cartridge. Insert the new cartridge and lock the lever into place. Shut the front cover and the side cover.
   
5. Power off the unit and power it on again if the copier displays a message reading "LSU Error." A problem has occurred with the Laser Scanning Unit. If the problem persists, call for a service.
   

Replace the toner: Always use the smart card provided with the new Print Cartridge when replacing the cartridge. The smart card contains the information necessary to reset the level of Toner. Replacing the cartridge without using the smart card may result in the consumable management system being inaccurate.

1. Insert the smart card provided with the new Print Cartridge into the smart card reader. A "Change Toner?" message will be displayed.
   
   
   
   
2. Press the [OK] button. An "Open Front Cover Replace Toner" message will be displayed.
3. Push on the left and right side of the Front Cover and simultaneously lower the cover.
   
   
   
   
   
   
4. Grasp the handle on the Print Cartridge, and then raise and remove the cartridge from the machine.
   
   
   
   
   
   
5. Unpack the new cartridge, and then insert the cartridge into the machine.
   
   
   
   
   
   
6. Close the Front Cover. A "Have You Changed the Toner?" message will be displayed.
   
   
   
   
7. Press the [OK] button. A "Please Wait" message will be displayed while the machine reads the smart card, and then a "New Toner Remove Card" message will be displayed.
8. Remove the smart card from the reader and dispose of the card as normal office waste.
   
   NOTE: If the smart card has been used with a previous installation of a Print Cartridge, a "Remove Card Already Used" message will be displayed. The smart card can only be used once. Make sure to use the card that came with the new cartridge.

Remove the cartridges from the printer, then close the covers. Unplug the printer from the power source. Plug it back in after 10-15 seconds. Check if "cover is open" message is still coming up on the display. If yes, the cover sensor may have gotten stuck when you opened the printer to change the cartridges. Try to exercise the lever to release the tension. If problem persists, I advise you to call Lexmark. If not, proceed on reloading the cartridges. Close the covers. Let it print the alignment page all the way through without cancelling it. Hope this helps. If you need more assistance, leave a comment and I'll get back to it. Thanks.

To reset the sensor after installing a new toner cartridge follow these steps. 1. With unit powered On, open the front cover. 2. Press the “Options” key. Display will show “Replace Drum?” 3. Press “Start” key. 4. Press 1,0 . 5. Display will show “Accepted” for approximately 2 seconds. Then display will change to “Cover Open”. 6. Close cover and see if Toner Life End error message has gone.
Try this. We are Brother authorized.

To reset the sensor after installing a new toner cartridge follow these steps.
1. With unit powered On, open the front cover.
2. Press the "Options" key. Display will show "Replace Drum?"
3. Press "Start" key.
4. Press 1,0 .
5. Display will show "Accepted" for approximately 2 seconds. Then display will change to "Cover Open".
6. Close cover and see if Toner Life End error message has gone.
Please note that this must be done with a new cartridge so the unit will see that there is toner in the cartridge.

Open the printer cover and check to make sure only one Yellow cartridge is installed. If so, try the following:
Remove each of the other cartridges, one at a time as necessary and see if the error message changes. Start by lifting the cover, then wait for the printhead to move to the left so you can access the cartridges inside. Pull out one of the other cartridges ( not Y) by pushing its front tab back then close the cover. Check the display, repeat as necessary. The error should have changed to U043 (bad or missing cartridge) once you remove the bad cartridge. When you replace it, the printer should work. My guess is the Magenta or Cyan cartridge is causing your error.

Make sure you have a new ink cartridge before you begin. You must install new cartridges immediately after removing the old ones.
Follow the steps below to replace one or more ink cartridges that are expended:

1. Turn on the printer.
2. If a cartridge is low or expended, you see a message on the display screen. Note which cartridges need to be replaced and press OK.
3. Open the scanner, then open the cartridge cover.
4. Squeeze the tab on the cartridge and lift it up. Dispose of it carefully. Do not take the used cartridge apart or try to refill it.
5. Remove the cartridge from the package, but be careful not to touch the green chip on the edge.
6. Remove the yellow tape from the bottom of the ink cartridge.
   
   Caution: Do not remove any other labels or seals, or ink will leak.
   
   
7. Insert the new ink cartridge into the holder and push it down until it clicks into place.
8. Once you replace all the cartridges that need replacing, close the cartridge cover and push it down until it clicks into place.
9. Close the scanner.
10. Press OK to begin charging the ink. This takes about 2 minutes. When you see a completion message on the display screen, ink charging is finished.

Caution: To conserve ink, never turn off the printer while ink is charging. If you see an ink replacement message on the display screen, press OK and press down all the cartridges securely

That usually means some sensor giving you trouble.

This is what brother recomends:

How do I clear the message Cover Open or Please Close Cover from the display?


The message Cover Open or Pls Close Cover may appear if the front cover
for the drum was not closed securely. Verify the cover is closed
securely by pressing the cover release button located in the front of
the unit below the Output Tray Support Flap and open the front cover.
Close the cover until it clicks into place.

If the message continues to appear on the display verify the drum and
toner assembly is installed correctly by following the steps listed
below:

1. Press the cover release button located in the front of the unit and
open the front cover.

2. Remove the drum unit and toner cartridge from the unit by lifting it
up and out. Place it on a drop cloth or disposable paper to avoid
scattering toner.

3. Hold down the blue lock lever located on the right side of the drum
and lift the toner cartridge out of the drum unit.

4. Reinstall the toner cartridge into the drum unit by inserting it in
the drum until it clicks into place

5. Reinstall the drum unit into the unit. Make sure it is securely in
place.

6. Close the cover until it clicks into place


If that doesn't fix it, I guess you will have to talk to their support people.


Good luck!

Please review the excerpt from HP technical support website http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00489814&lc=en&cc=us&dlc=en&product=441240&rule=31105&lang=en Use the instructions below to resolve the issue by restarting the product. 1. Disconnect the Universal Serial Bus (USB) cable from the back of the product, but leave the product turned on. 2. Open the cover of the product and remove the print cartridges. 3. Close the cover and wait for the Insert Ink Cartridges message to display. 4. Disconnect the power cord from the back of the product and wait for one minute. 5. Reconnect the power cord. If the product does not automatically turn on, press the Power button. 6. Open the cover and reinsert the print cartridges. 7. Close the cover. If prompted, print a calibration page. 8. Reconnect the USB cable, and try to print a print job from the computer. If these steps did not resolve the issue, contact HP technical support for assistance.