I've been having an issue with the wife's computer. It's an old Athlon 1200.
It was fine on idle but as soon as you tried to run something, probable within 15 min it would shut off. I checked the cpu temp and it was around 60c I think. I checked the heat sink/fan. The fan was running fine but had alot of crud in it. So after unplugging it, I took the hs/fan off and cleaned it out. I then put it back on. Now the computer will only stay on 15-20 sec at the most.
I checked to make sure I had the hs/fan on properly and it is. I didn't reapply any thermal compound though. Should the cpu not run longer than that even if it had no fan/hs installed?
Just looking for ideas.
Also before it's mentioned, I'm building a new box to replace this, but I'd like to have the kids use this one if possible.
1) You really should have cleaned off the old thermal interface material, be it paste or pad, and applied new.
2) It's entirely possible that the heatsink isn't seated perfectly flat to the CPU. Older Athlons especially were notorious for giving people difficulty with that.
3) There is the possibility that you've managed to fry your CPU. Depending on the hardware involved, it may have no thermal protection to shut it down in time. (And by the sounding of things, your hardware seems old enough to not have this.)
I'd say, try cleaning the old TIM off with rubbing alcohol, grab any old thermal paste from a nearby shop, apply a little bead of it, spread it with a credit card, and make sure that when you put the heastsink back on that it's really sitting flat against the CPU. If it still doesn't work after that, take it to a pro because you may be SOL.