AMD K6-2, slightly underclocked, turns off spontaneously. The only thing I suspect is heat damage to the CPU or mainboard, and want to confirm if possible before I buy a replacement.

Turn-off is independent of activity, OS, and ambient temperature (happens in Windows, Linux, with and without A/C). System has 2 hard drives. The whole thing is about 3-4 years old.

It is not a power supply problem, as I changed the SMPS with no effect. The power switch seems ok, I will check the reset button later.

Possibly related: Linux requires the no-hlt boot parameter, otherwise kernel oops. At least with 2.2.x kernels.