All games crash -- why?

Just about every "real" I have tried on my computer crashes and burns. I'm trying Age of Empires III, Bioshock, The Witcher, and Dragon Age. Some of them run for a bit (in e.g. Bioshock at 1024x768), and then after a few minutes of game time my screen resets to my desktop at 1680x1050, with a large black area for the minimized game, informing me that the game's .exe has faulted and asking if I'd like to tell MS about the problem. The Witcher never even gets to the opening screen -- it crashes about 5 seconds after I double-click. Sometimes, Bioshock and Age of Empires III will play for a bit, and then go into a loop with the last half second of sound replaying endlessly -- the only solution to this is to power off my computer and reboot.

These problems were happening with my old x1950 pro but they're also happening with my new 4770. I uninstalled and reinstalled the video drivers. I also updated to the latest sound drivers. None of this works.

Help?


Specs:

Gigabyte P35-DS3R (built-in realtek 5.1 sound + drivers)
4 Gigs DDR2 RAM
Coolermaster eXtremePower 500 watts
Pick one: x1950 PRO or new Diamond 4770 (both 512m)
The DS3R has on-board RAID and I have two 500gig drives mirrored.

Should have added - running WinXP, service pack 2.

If you're still on SP2 I assume you haven't done a clean build for quite some time. All the time you spend trying to narrow down the issue would be saved by backing up and doing a clean build, imo.

It looks like it's to do with your psu. the 500w is not giving you enough power to run your graphics card. Try upgrading your psu to a 600w+