Overheating Graphic Card

Been having trouble with my graphic card overheating, and I'm still having trouble understanding why. I built this computer about 6 months ago, and everything was fine till about 4 weeks ago when I started playing Stalker. At first everything was going good, but about 10 minutes into the game a beeping noise started going, so this window pops up saying the card is too hot and it's going to under-clock the card (ATI 1900XT) to help lower the temperature.

At first I was baffled, because this had never happen to me before. I decided to just turn the game off and see if I could solve the problem, which I thought I did. I opened up the case and saw some dust build up, so I cleaned everything out and tried playing the game once again. This time the game didn't overheat and everything was fine and dandy. So today I pick up Oblivion, but right when I'm at the character creation screen, I get the dang beeping noise again saying it's going to under-clock the card to help with the overheating. It can't be dust, because it's all cleaned out now, so it has to be something else, but I don't have a clue on what it is. Maybe I need to take the heat-sink off the card and reapply the thermal paste? That's about the only thing I can think of right now.

If more information is needed, I posted my setup here, so here's a LINK to it. Also, my specs are in my sig. Any help would be greatly appreciated. Thanks!

have you got the latest drivers installed for the graphics card it might be the drivers thinking its overheating. try downloading Everest and check the temp on there. if it is overheating make sure you have good air flow in your case installing a few fans will help or just buy a new heatsink for the GPU adam0926

Latest drivers are installed. I downloaded Everest, but it's not telling me the temperature of the card for some odd reason. I think I'm just gonna uninstall the driver and reinstall them again and see what happens from there.