- sure not under oc , do Clear Cmos
- check fan cpu spinning
- test ram with memtest86+ (use 1 stick also try in different slot )
Other posible then check conection keyboard, check cable from psu to mobo, try use other cable HDD
I've seen hanging chads, hanging plants, hanging are...but why hang a PC? Did it offend you?
On a more serious note, we are talking a hard freeze, right? Not a BSOD or lockup and immediate automatic reboot? Did you recently install any new hardware, such as a graphic card, sound card etc.? Have you installed any new USB devices? Did your machine run Windows update sometime in the night? The first thing I would do it disconnect all USB peripherals except the keyboard and mouse and see if you are still locking up.