@greg2
As this is a Photosmart 6510 I'd advise heading over to the Consumer forum at the link below...
http://h30434.www3.hp.com/t5/Ink-Toner-Cartridge-Printhead-Issues/bd-p/Ink
Is your printer out of warranty? I take it you've tried all the usual troubleshooting steps like running a printhead clean etc?