[QUOTE=Mojo31;21938273]Printers are disposable these days. However, a new print head may fix it up, but it will cost you almost as much as a new printer.
Here's a discussion of some things you might try first:
Solved: Photosmart 6520 will not print in black after installing new... - HP Support Community -
I would try a different black cartridge. There is a chip embedded in the cartridge that holds a date when it was activated. Even if it has ink, it will tell the printer its empty.