HP Officejet Pro L7780 has stopped printing in black after changing yellow cartridge. Black is barely showing in spots. Have cleaned the heads and restarted twice and black cartridge is almost new, at least 3/4's full. Also align printer failed when going through process. Thanks, JW

I have to ask this question of you, just to make sure this is not an issue. Are you using a factory new ink or toner cartridge?
Please consider the following:
If you are using a refilled or third party cartridges that may well be your problem. Most manufacturers build logic into their products to prevent the use of “Other Equipment Manufactured” cartridges as well as re-filled cartridges.
They do this to prevent problems from contaminated inks or toner causing problems with print quality or damaging the physical printhead or photo conductors.
If you are using factory new ink or toner cartridges, then please call the manufacturer’s Technical Support for assistance with the warranty on the cartridges
Don