PC hardware: System Instability!

System Instability!

I recently bought a Sapphire x1950Pro PCI-E. I uninstalled my onboard card's drivers,went to the ATI website, updatedd the drivers, got CCC 7.7.

I start up oblivion, change the video settings, start playing. After about 20 minutes, the game crashes and it shows the "This program has encountered a problem and needs to close" thingy. then I start half life 2 lost coast. This time, 5 minutes into the game, it crashes. I tried theHitman:BM demo and it crashed. I tried again, and I played it all the way through with no problems. Then it started geting worse, whenXP started up, some 4 or five programs failed to start up. Even Internet Explorer crashes every once in a while. Then it went from "X program has encountered a problem", to "failed to start X.dll". I even got the blue screen that says "Windows has shutdown because of a system error. If this is the first time you see this screen... blahblahblah"

I tried using the MSI Live update to look for updated BIOS but it says that version 1.00 is the latest.

this is my motherboard
http://www.msi-computer.ca/product_info.php?cPath=22_35&products_id=63

I've tried a system restore, so it is not a virus. What else could cause so much crashing?
I am guessing it is my RAM, but I've been using it for 5 months with no problems at all.
Is there some sort of utility that could help me find the problem?