Describe how you change the ink for a HP PSC 750?

1- Open the printer
2- Remove the ink cartridges from the print head.
3- Use cotton swabs dipped in hot water to thoroughly clean the print head.
4- Repeat this until there is no ink residue coming off on the cotton swab.
5- Once finished, allow to dry and replace the cartridges

Yes you have to use both the black and color cartridge in order for the printer to work. Both cartridges need a good supply of ink in them to, or it wil not print.

Dear,
Please check this link and you will find how to do it:
http://bizsupport1.austin.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=295845&prodTypeId=18972&objectID=c01367419&printver=true
Regards, Eng.Ghassan Alasmar

Hello
Have a look at the link below, it should assist you in solving your problem.
Click HERE.
Kind regards
Michel

1. Allow your injet printer to run entirely out of ink. Unless the quality of your images is suffering, there is no problem with letting your ink run low.
2. Open the printer door. It should fold from the top down toward the tray. When it is open, it should expose the inner workings of the printer.
3. Press the change cartridge button. It is at the top of the printer next to the power button.
4. Pull on the green top of the inkjet ink cartridge and remove it up and out of its holder. Do this gently so the printer is not damaged in the process.
5. Recycle the empty inkjet cartridge or have it refilled at an ink refilling center.
6. Carefully remove the tape from the refilled or new inkjet ink cartridge and insert the cartridge in the same orientation as the one you removed.
7. Push on the green top until the cartridge snaps into place, press the cartridge change button and close the printer door.

Did you make sure you removed the plastic tape protection before installing the cartridge? Check to see if there is anything on the bottom of the unit. It could be the problem. Check the install instructions.

Need to replace all print head with error or nozzles block
and try for alignment
once the page is printed it needs to be scanned to save alignment
if still get same message need to check for scanner functionality

With power on, simply lift up from the hatch located on the front of the unit. The ink jet will slide to the middle position.

Ink Cartridge Supplies for the HP PSC 750
Description
C6615A Black Ink Cartridge (HP #15)
C6578AN Color Ink Cartridge (HP #78)



That's right according to the above info
Try
Normal 0 Driver could be corrupt.
Disconnect the printer or at least be sure it is turned off. I'd do both and reinstall the CD software program that came with the printer. When the software program asks you to connect the printer to the USB port, do so and it should again work properly.
Hope this helps. Bud

Husband fixed it. :-)