If this is not the only program and you have not updated your drivers you should simply update your drivers.
Careful when telling people to update their drivers. There can be massive performance decrease and loss of functionality when you put on the latest and "greatest" driver with even a slightly dated video card. As an example, my older nVidia 6800 works best with the 61.77 drivers. If I updated them to the newest ones, I doubt AH would run properly.
If the game was functioning and drivers were not changed, drivers should not be an issue. Overheating of the GPU comes to mind though. Have a look at how much dust has built up on the video card, especially the heatsink. Check if the heatsink is beginning to fall off. (Yes, I've heard stories of people opening their cases and finding the aluminum sitting on the bottom)