Custom Computer Crashing

[otistheguard]

Hey everybody, this problem has been plaguing me for weeks. My computer will crash at random while loading maps, games, web pages, and windows. It only happens when loading, I don't have any trouble playing the game. The screen will turn black, or sometimes different colors with vertical bars. Any sound that was playing will continue playing for a few seconds. I do not get any error messages or anything unusual in the Event Viewer.

Here are my specs:
DVD Burner: SAMSUNG | SH-S222A
Hard drive: 250G|SAMG 16M SATA HD253GJ - OEM
Video card: VGA SAPPHIRE 100287VGAL HD5670 512M
Operating System: WIN HOME PREM 7 64-BIT ENG 1PK DSP
Motherboard: GIGABYTE|GA-MA785GM-US2H RT
Processpr: AMD|ATH II X3 435 AM3 R
Memory: 2GBx2|GSK F2-6400CL5D-4GBNT GSKILL brand
Power Supply: TT | W0070RUC 430W RTL
Case: TT|VJ60001N2Z BK RT
Netgear WLAN USB adapter

I've done the following:
Flashed the BIOS
Used one memory card at a time
Messed with BIOS settings related to memory like CAS latency
Turned off the onboard VGA
Left my case open with a fan on it
Reformatted the computer
Ran windows memory test, extended version with no errors

I had the PCI video card unplugged for awhile with no problem, but I didn't use it enough to get a crash.

Please, if you have any ideas please let me know. This is starting to become very frustrating.

 

[huron]

Please list your system specs - it gives us a good place to start as well.

 

[otistheguard]

OP editted to make the specs more obvious. On another forum, a Gigabyte rep suggested it is the video card.