Can't Game In Vista Or Xp

I've got a Gateway FX7026 pc.
24" lcd monitor
Q9300 quad cpu 2.5ghz
nvidia gf 8800 512mb
4gb ram

I can't play Quake wars enemy territory, can't play cyris, battlefield 2 demo won't work. All these are demo. Age of empires 3 and war chiefs work just fine.

in the games that don't work they will eventually lock up after a minute to 3 minutes. you also see tons of weird very fast moving lines all over the screen. not sure how to describe it. can take a screenshot if possible.

Temp is fine im sure as is ram etc.

is this a video card being dead issue or what could it be? i am guessing hardware cus this happens in more then one game and the same thing and it happens in both vista and xp. i have prebuilt with the pc it came with vista home premium sp1 64bit and i installed on the second hard drive xp sp3 pro and both oses and the same games have the same issues.

I installed newest nvidia 64bit drivers for vista and the issue still happened.

I'm totally clueless here. My guess is i'll have to take it where I got it for a replacement which is fine as i'm under warranty for 2 total years from when i bought this pc a few months ago.

doing a recovery on the pc doesn't help either. I'm also not running any software other then the game.

i don't have any other issues on the pc, just these ones mentioned in here.