HP 722C cartrige light flash will not print.

I think the problem is in the cartridge or cartridge assembly. You said that repalacing the cartrdige don't repair the problem.

Maybe there are dirty contacts in the cartrdige holder. Take a brush (like a toothbrush) and clean the contacts of the cartridge holder.

Note that even new cartrdiges can be damaged. If you put a clogged cartrdige the printer refuse to print and the orange led is blinking.