BFG 6600GT dying?

Hey everyone.

This is kind of a weird problem, so I hope I will find the answers I need

Anyways, here goes. I recently upgraded my PC (bought a new mobo, CPU and ram) which are the Asus M2N-E, AMD x2 4600+ and OCZ PC6400 DDR2 ram. When everything was installed properly, I noticed that when I was in Windows my PC would freeze (hard lock) at random times and I was forced to reboot.
Let me backtrack for a second. With my previous PC before I upgraded, this happened IN-GAME maybe 3 or 4 times max (and by this I mean the hard-lock freezing). This happened before I upgraded too.
I've had this new PC for about a month now, and I'm still experiencing these freezing problems however they do not occur in-game, they happen in Windows. I find it happens a lot if I'm downloading with Firefox and multi-tasking (weird).
Within the past few weeks, I've noticed when I exit out of Quake (yes, the original Quake) my PC will freeze for mabe 5-10 seconds and I will either see vertical lines of gray and white, or just a scrambled red screen. I know this could be because of the video card.

My question is, can the video card also cause these random Windows freezes? Any help would be MUCH appreciated.

And it is NOT temperature related! I checked and all the temps are perfect!

What you describe sounds exactly like when my 9600xt died. So yes, it could very well be a video card issue.

Logical2u: Thanks for the quick reply.
My PSU is an Antec Truecolor 2.0 480W, so I don't think it could really be a power issue - but then again maybe it could?
Hard drive is a Western Digital Caviar WD2500KS 250GB.

the_irish_fly: It's not my RAM because I ran memtest and came back with 0 errors.

Yeah I guess so. Just so weird that it causes Windows to crash randomly.

I also just ran CHKDSK just to make sure. How do I check the results from it to see if there were any errors?