When I turn on my computer after leaving it to rest for 15+ minutes, it will POST and sometimes freeze while loading Windows. 50% of the time, it will freeze for a few minutes once it boots Windows. If it gets past those few minutes it usually won't freeze for at least a few hours, if at all.
When it doesn't POST, the fans just keep spinning infinitely. There're no beep codes or anything, just fans continue to spin with nothing displayed on screen.
If I remove all RAMsticks for example, the computer will usually still make no sounds but the fans will spin forever with no display. If the computer was going to Post anyway, I'll get the standard beep code indicating a ram problem. This is the same with each piece of hardware, and with nothing but the CPU plugged in the results are the same. I'm thinking this must be the psu or the motherboard, but both of these components are new and I don't have another psu lying around to test.
Also CPU-z reports the CPU speed as 1,6 GHz no matter what, even with Intel burn test running and speedstep disabled. Tempratures on all devices are well within the normal range.
Some specs that might prove useful:
i7-920GTX580P6x58d-e750W PSU
The motherboard and power-supply are both new.