Aspire 5100 problem 1 - shuts down in 90 seconds on DOS or BIOS mode

If I boot either into DOS, or just hit F2 during startup and go into edit mode of the BIOS settings, the machine shuts down in about 90 seconds. It's awfully quiet, meaning it's probably that the fans aren't running and the temperature gets too high, but that's a guess.

Not that I plan on spending a lot of time in DOS or updating the BIOS, but it's a malfunction (one of a few) that I'd rather not have to deal with. Any ideas?

(It's got Vista (Factory OEM), upgraded to SP1, but this isn't something that happens under Windows).

Thanks in advance

 

FYI, I never was in there often enough to really pay attention that it was chronic, but the problem has always been there, including prior to my BIOS update from 2.87 to 3.13. Thankfully, the BIOS update, done via a USB based DOS boot disk, finished in less than 90 seconds, because it sure looked like the computer shut down unexpectedly during that BIOS update process.

 

Overheating would be my guess. I had an AMD powered Acer that would do similar, and again worked fine in Windows. Cleaned the fluff out the heatsink and it worked perfectly.

The fan might be very quiet, but it might have failed. And the fins on the heatsink assembly might be blocked. Also probably worth cleaning the old thermal compound off the h/s and CPU and applying new.