Computer POSTs...Sometimes

Hello all. Long time reader, first time poster.

Anyways, I have a rather unfortunate problem on my hands. My computer shut off on me one day without warning and has proceeded to randomly turn off since. Sometimes I have to reset the CMOS in order for it to POST.

Right now I have the mobo out on a cardboard box with only the video card and one stick of memory installed. I have the 8 and 24-pin cables gong to the mobo as well as a 6 and 8-pin cable to the video card. Initially it wouldn't POST at all. I get the dreaded red CPU error light on the mobo and nothing powers on. I reset the CMOS and it's POSTing....for now.

I've been through there before and my comp would work for the day, and after several hours shut off again.Last night everything was fine. I turned it off normally and then this morning it wouldn't boot! I'm guessing it's the mobo, but anyone got any other ideas?

My first thought was overheating, but my temps are fine with CPU just under 40C and GPU a tad higher. I switched my PSU with my friends and the same issue keeps coming back


Thanks in advanced!!

BTW here are my specs:
Windows 7 Ultimate x64
ASUS Rampage III Gene LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 Micro ATX Intel Motherboard
Intel Core i7-930 Bloomfield 2.8GHz LGA 1366 130W
ZOTAC AMP! ZT-40102-10P GeForce GTX 480 (Fermi) 1536MB 384-bit GDDR5 PCI Express 2.0 x16
G.SKILL PI Series 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
CORSAIR Enthusiast Series CMPSU-850TX 850W ATX12V v2.2 / EPS12V v2.91
Corsair Force Series GT CSSD-F240GBGT-BK 2.5" 240GB SATA III MLC Internal Solid State Drive

Thanks for the reply!

Just tried a new one and the comp shut off on me after maybe 5 mins. I was able to stay on for a few hours without crashing earlier, but now its more like 5 mins. I'm waiting for a new mobo from ASUS, but who knows if that's whats really going on.

Any other ideas?

Could it possibly be a PSU issue as well? Normally I'm used to PSU issues where the comp won't even turn on, let alone stay on and turn off on just whenever.

I know i said I used a friends PSU, but that was before the first time I cleared the CMOS. Not sure if that has anything to do with it. The only thing I ever did in the BIOS besides set the boot order was OC my memory to 1600MHz, and that was several months ago.

Thanks again, really hope there's a solution out there.