I measured temp using MobileMeter, and the temp never gets above the 40s when it croaks, so I don't think that is the problem--at least not the temperature that MobMeter is measuring. I have even put my laptop in the fridge for 30 minutes, and then started it up (on AC), run NAV Full Sys Check, and it does the same poweroff. Spybot never finishes its run, but powers off on different checks (I've video taped the bottom line to verify that).
By the way, after it powers off, when I power it back up, it comes up, presents the first boot sequence routine (the screen that tells you, "Push [F2] for Setup . . .", etc.), and then goes to a totally black screen and stays there. The laptop cannot be powered off using the button. I have to remove the AC cord and battery, and only then does it completely boot.
I updated to the BIOS 1.80 from Toshiba successfully--or at least I think I did. However, I may not have and here is why I say that: After the 9th program finishes its final validation step of the BIOS change process, the laptop powers off spontaneously. And I don't know if that is normal-- is it? I'd think not; you'd think it would say, "You have successfully installed BIOS 1.80," or something like that.
Suggestions? Is someone going to tell me to remove dustbunnies from inside? That would mean that the suggestor doesn't think MobileMeter is measuring temp correctly, wouldn't it? I'm thinking it is the CPU or motherboard. The unit is off warranty (bought in late 2003), so I don't think it is worth it to replace the motherboard.