Initially I thought that the problem was my video card because every game that I opened would crash after about ten minutes. But after a post in the Graphix Card forum on this site, many people suggested that the problem sounded like unstable memory, and that I do the memtest from memtest.org. I did that and I got 60 k errors after 10 minutes.
I checked and double checked, the ram is definitely configured properly in the bios. But it just doesnt sound like a ram error to me.. because my other apps dont crash at all. Wouldn't firefox crash, or even windows 7 crash if the ram was the problem? not just games? anyways..
I was wondering if that definitely means that my ram is actually BAD, rather than some configuration mistake that I missed. There were many options to configure in the BIOS of my memory, most of which I didn't understand so I left them all on auto. But I manually configured it to 8-8-8-21, and 1.5v which is what it needs.