If it is a heat problem, I think it would happen after 10-15 minutes maximum. If I ran many programs together, and the PC case wall is fastened, the CPU warning start ringing after about 3-5 minutes when I start FS, and the graphics card start really spinning. When it happens I used to take off the case wall, and the machine get fresh air, that usually solve the problem.
But again, I think overheating do not come after 30 minutes only. I think it is rather a software, or power supply error. Unfotunately these things mostly unrecognizable.
Once I had a fuel gauge at many panels, that used to crash my system about 5-10 minutes after starting FS. It was an incompatibility with some XP parts, and I got a patch from the author that solved the problem.
Try to locate the problem, by analyzing more deeply the situation...