Generic black ink cartridge not printing on hp officejet pro L7780

You should take it back and exchange it or read on below.

Most modern cartridges have an ink level chip built on to them.
Should the level drop below 25% then most of these chips lock up and will not reset.
Re-filling them will have no effect
If you are lucky you should be able to find either a resetter around on the internet
OR
Even better empty cartridges that never need to be reset.

The second option is my preference

I realise these are not for your specific printer but there are others listed on both those sites as well

Pls get a genuine hp ink for ur printer