My computer just shuts itself off

[Conphas]

I have the temp warning set, they never go off, and when I reboot my computer, the temps are all well below the "warning" temps...

At first, I thought it was a power supply problem so I replaced the Power supply with a Corsair
(note on power supply: The big 24/20 set pins only had the 20 plugged into the motherboard originally even though it looks as though it would take a 24 pin. I copied this, should I plug the other 4 pins in???)

Second thought was a crappy virus so I did a complete reformat... no luck

I'm worried I have a short somewhere. Any ideas what could be causing the computer to just shut down?
No warning sounds or anything. I could be surfing the web, playing my game, listening to music... it just shuts off. The one time I tried to reboot immediately, it wouldn't even make it through the startup screen(s). So I usually wait a good 10-20min before I attempt a reboot. Never seems to have a problem booting up if I give it some time.

Any help would be appreciated
Thanks

 

[tiraides]

If you believe that you have a short, take the motherboard out of the case, check for any loose screws, and remove any additional motherboard standoffs that you aren't using (to keep the motherboard in place).

In the meanwhile, try booting the motherboard outside of the case to eliminate any possibilities that something else could be causing it to go off.