If you want, you could open up your computer and check if there dust or something clogging up the GPU vents (if you don't know how, don't), though I still recommend that you try and get that ATI program working.
Keep in mind that I put overheating as a unlikely cause, so it may or may not be overheating, though it doesn't hurt to check and I don't really have any other ideas (except if your GPU or other hardware is faulty, but that's even less likely and cannot be fixed) at this point. :\