Just did it again, with the cover off. Max temp now says 73. Putting a fan on it now too to see how it acts. Maybe should replace GPU? It's been fine for 3+ years, in exactly the same configuration, now this.
It's an NVIDIA Quadro NVS 290. The computer is a desktop model, and I'd like to spend $100 max, if possible. I don't think Iy should take anything fancy. This computer will never be used for gaming or video.