Graphic bugs in games

[piranha68386]

hello people, first i will let you know my configuration of my pc. i have xfx 512 mb 8800 gt alhadog editon graphic card, 2*1gb ddr2 800fsp transcend ram, 3600+ amd x2 , jetway m2a692 gdg mother board , zebronics -600w smps and 500 gb sata hard disk . i have installed windows xp with sp 3 and have updated all the drivers. the problem i am getting is that some games work very fast(like fast forwarding) and some games work very slow(for every 10 secs the game will work for one second and freeze for the rest of the 10 secs). games which are moving fast are nfs most wanted,carbon , counter strike. game which is going very slow is gta 4 . this problem starts only after some 10 mins of usage of pc from the start up . i tried cleaning up the dust from the cards which proved to be no use . help me plz thanks in advance

 

[piranha68386]

i also tried 3d mark 06 , i didnt take back up of the results . but i remember the result of the video which was jus 1-2 fps, whereas the others were around 30-40 i guess