Computer Shuts off Randomly

[reiger]

When I went to college 6 months ago. I brought my desktop with me, worked fine before I left. Got to school set it up, and when I'm running many processes on my computer or loading up a game it will turn off. Then after that some times won't even turn back on. I thought maybe it was my power supply since the one I had was the minimum power I needed, and was old. So I bought a brand new PSU with more power, and the same problem is happening.

Here is my specs

Motherboard: Gigabyte S Series P35-DS3R
PSU:Corsair TX 850 W
Processor: Intel(R) Core(TM)2 Duo CPU E6750 @ 2.66GHz (2 CPUs)
Memory: 4 Gigs of Ram
Hard Drive: 800 Gig HD Total
Video Card: NVIDIA GeForce 8800 GT

I tried many different ideas to fix it. I thought it was either the power supply was going bad, or over heating. But I got a new power supply and the heating is normal

UPDATE:
Alright, I just removed everything from my computer, took motherboard out and processor out. Put it all back in and made sure everything was connected, and connected tightly. Computer turned on, and was loading everything. Tested loading a game, and right before the map loaded up it crashed. Then turned computer right back on, and turned off in a minute or so.

I'm going try get all my information on my backup hard drive then reformat. If that doesn't work any idea?

 

[kimsland]

I'm going try get all my information on my backup hard drive then reformat. If that doesn't work any idea?

For a fault that first started happening 6 months ago!
Yes please do a clean install of Windows to confirm its not software related
Note: A clean install means removing the Partition(s)

Obviously this is Vista 64Bit OS ?
I suspect that you may have a Gigabyte Restore disc (or image on your hard drive) with this computer as well?
Then try that
At least then you will know if its hardware related (as you suspect already that it is)