In seek on gaming help (graphics card problem)

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Here are my specs before anything..

RADEON 9800 PRO graphics card
2 gigs of ram
200 gig Harddrive
Athalon processor

Okay, not too long ago my computer was shutting down after playing any of my games that require to use my graphics card a little bit - (WOW, HL2, CS:S, WC3, ect.) and I cracked open my computer to find that it was rather dusty - (this made sense) I cleaned out all of the dust and then ran my computer and everything looked fine, but when I went to play my games there were these random spurts of lag (while I had a ping of 30-40, and a fps of 85+) this didn't make any sense to me..I tried turning down my graphic resolution (in game) and it still had the same laggy-ness. (When I moved around too fast or changed the camera views) I went online and download the drivers for my graphics card. - no such luck! - I'm wondering if my graphics card had gotten damaged ( from the overheating shutdowns) or should I take it out and try more dusting / cleaning and then put it back in?

Note: Before all of this happened my graphics card could run no problem any game that I owned - with high resolution.