Help i cant play any games

hey i recently made my first gaming computer about week ago. everything was going fine i could play crysis on low and cs:s no problems. but recently i havent been able to play ANY of my games. after a few minutes i get a windows error and taken back to my desktop and i got these wierd lines going across my screen. now im assuming its my video card because everything ive tried( reinstalling drivers taking the card out and putting it back in stuff like that) have not worked any ideas?

right now im running on
Intel Core2 CPU 6600 2.40GHz
nvidia 8600 GTS 256 mb
1g of ddr2 ram (i had 2 but one of the sticks was defective and ive yet to fix that)
windows xp

 

It sounds like the video card is over heating.
The first thing to check would be to make sure that the fan on the video card is spinning.

 

i just checked its spinning

update: also when i play WoW and crysis during the few minutes i can play sometimes i fall through the ground... maybe that will help figure out the problem

 

Whats the temperature of your card?

 

right now its averaged at about 66-68c i think

 

Woo, its sounds like you video card is overheating if its in idle.

Try to spray out the dusts using air compressor.

 

there is no dust i just built the computer

 

what is the error? could you post it here?