Hi I have also purchased this printer it's set up on wifi and it's been locking up when not in use. Rather than phone HP and speak to some call center guy with no technical experience I began to mess with what few settings this printer has.
The problem seems to stem from the print server going to sleep and not waking when prompted by the LAN or even the buttons itself.
So far touch wood i seem to have fixed my problem. I realized that the printer was pulling an automatic IP address so i changed it to manual IP address and inserted my LAN details. Viola! it seems to have worked so far. The screen still goes off after 10-20 mins but will restart on command from the pc or mac and via the screen buttons. Hope this works for you guys too.
Just got home and checked it's been working fine for 24hours now lock up free.