thermal event

Bob. Thanks for reply.
Gone into the processor and nothing I can see bust/loose,also cleaned away dust.
The problem is a bit strange in that it only happens on a start up after a long time switched off,like morning after being off all night.
I tried just as a test to turn off during day, leave it an hour and start up and no problem.

( What happens is_in am start up as normal, after about a minute it shuts down.
I start up again and the screen tells me the previous shut down was caused by a thermal event which may be associated with a recent program addition if I want to continue press f1 f2 and restart, which I do.Usually have do do this a few times, eventually restarts ok and runs all day
George

First, are you sure it's a thermal even? This problem could be caused by any one of several problems and are all relatively easy to fix.

To check if it is indeed a thermal even, try running your machine with the case open, that will allow more and cooler air inside, and stop this problem, solution, get a better heatsink and fans.

Another problem may be the PSU, what is your rated at and have you upgraded the machine recently? Solution, if necessary go for the highest wattage output your pocket can stand.

Yet another problem may be the RAM, now and then it can have this effect, question, how long have you had it in the machine, the solution here may be to replace it.

Even worse, whilst you've got the case open (and with the power off) check the capacitors on the motherboard, if they are cylindrical with a flat top, all's well, BUT if any are bulging, either at the side or on top, then it's time to think seriously about a new board.

Thanks Themisive. I dont know if its a thermal event, the screen tells me it is when I start up again.
Ill try all you suggest
George

The thermal paste between the CPU chip and its heat sink does dry out after being baked by the heat generated. Buy a tube from Radio Shack, remove the heat sink, scrape off the old junk (especially if it's caked) and apply a new layer before replacing the heat sink. That should help cool you CPU better. If you have a removable heat sink over your graphics chip, you may want to do the same there also.