Hey I have an HP photosmart printer 7700 series and I have a real problem. The printer itself will just up and freeze/lock and it won't respond to any kind of input from any computer. It also won't shut off by hitting the power button and none of the other buttons on the printer work either. The only thing I can do is unplug it and plug it back in. This only works some of the time.
That is a USB communications problem, I have come across it before. You need to arrange for the printer to be serviced. Is it under warranty? [less than 12months old?] If yes you can arrange a free service.
Call HP and they operate a swap out via courier [usually DPD Parceline] if you are in the UK. I am unsure as to the procedures HP use elsewhere.