Months ago my graphics card stopped working, so I broke out my backup 9400 GT and I've been using that to play games and such, but it has serious overheating problems and it never used to get this hot. It's idling currently at 73C underclocked and if I play any games like TF2 it hits 100C and stops working entirely until I restart my computer. With my case open it's the same and the only way to keep it from overheating is putting my computer on its side with a house fan blowing strait into it.
My old graphics card didn't do that and the 9400 GT never used to either. There's no dust and the fan is indeed working.