Some computer problems

Currently am running:

Intel Core i5 2500k @ stock 3.7
w/ 212+ running push/pull
AMD Radeon 6950
Asus Maximus Gene-Z Mobo
Intel 40g SSD-Im a cheapo 
WD black HD 1TB

And a Large Large case.. (Didn't know it was a micro mobo..)

My problem is my computer randomly shutting off all the time. I will log into a game and it will be okay for maybe about 3 minutes and then it will freeze up, my USB ports will stop working and then it will shut down.

I have been monitoring my CPU and GPU temps and they are staying very stable. CPU=40 on load. GPU=60 on load.

Would anybody have any ideas on this? It would be greatly appreciated... Thank you.