It could be your printer or something that is causing it to want to boot from your printer.
I've had that happen to a client recently. Their HP printer was trying to boot and it froze at the mobo screen and finally would go to windows xp after an hour.
Unplug everything but monitor, mouse, keybaord
and on the inside go to bare bones - mobo, hdd. take out vid card if possible.
if it boots normally,then slowly replace each component 1 by 1 until you find it freezes again. That component you just put back in is the culprit