so last week i replaced my aged 6600gt and got a 9800gt in preparation for sc2. my problem is it crashes and totally powers off my pc mid-game.

so far it hasnt crashed on warcraft 3 and work fine unless i play some games like sc2 beta, portal, doom3 roe. for normal non-gaming apps it hasnt died powered down ever.

one minute the sc2 beta (maxed out settings) would be running smoothly then suddenly slows down a whole lot before it returns to normal then a few minutes later everything just powers down as if the plug has been pulled.

i have a 500w power supply (not true-rate though), but i never had this problem with my previous videocard.

i tried to return the videocard so they tested it in 3Dmark 06 to test if it crashes there as a game would, however it apparently worked fine for the whole day stress-test(i only stayed the first 30mins to check the benchmark as i had work the rest of the day, and since it usually failed on or before 30min mark.)

btw my specs are

2gb of ram
1 primary drive and 1 secondary drive
1 optical drive/writer

I tried to isolate if it was the power supply by detaching the connections to the secondary drive and optical drive, but still ended up getting plugged out all the same.

First of all chech the temperature on your videocard. Use speedfan or everest or just simply touch the videocard - it might be overheated. Update drivers - it might cause problems as well.