Crashes on newly constructed comp

[Quarthex]

I very recently built my own computer for the first time, but I'm getting constant crashes and freezes when trying to download large video games from Steam. At first I used BlueScreenView and found that the NIC driver was potentially at fault. After trying different versions of the driver I was unable to solve the problem. Because I had just about nothing of value on the computer and it failed Prime95, I reformatted it.

It's still crashing or freezing when using Steam, but now BlueScreenView is not pointing to any specific driver (not highlighting anything in red). I tried Safe Mode w/ Networking and it crashes to BSoD while downloading in Steam too. My RAM turned up no errors on 5 passes of Memtest86+, but I only ran the test with both 2 GB sticks in simultaneously.

I've noticed that when it freezes I can still move the mouse. I'm not sure if that is always the case, but I can remember being able to move the mouse at least twice (out of maybe four or five freezes).

Here are the basic specs:

Windows 7 Home Premium 64-bit, which I installed myself.
The computer is under a week old, the current installation of the OS is a matter of hours old.
CPU: Intel i3-2100 @3.1GHz
PSU: Corsair 750W PSU
Motherboard: ASRock P67 Extreme4
Memory: 2x2GB G.Skill DDR3 1333 (PC3 10666)
GPU: 2x Radeon HD 6870
HDD: WD Caviar Black WD5002AALX

Any help would be greatly appreciated!

 

[Quarthex]

For what it is worth, I have removed one of the sticks of RAM and the computer has run without issue since then. This does not appear to be a Windows 7 issue at this point. I plan on getting the RAM replaced.