New HP 6100 Officejet Won't Print

Got new HP 6100 back in Dec 12. Ran okay. Kept getting error about yellow cartridge being bad. Replaced. Still had problem with enpty cartridge.

Replaced all 4 - blk, yell, mag, blue. Now printer will not print ANYTHING. No test pages from PC nor any self-test pages from within printer's firmware.

Any ideas?

Thanks