OK, basically, when I logon (either via windows XP welcome screen or business logon window) I immediatly logoff. It persists in safe mode. I had to reformat last time, and now it's doing it again. I swallowed my geeky pride and asked on this forum.

HELP APPRECIATED.

I found no reports or signs of malicious software beforehand, though that's likely what it is.

This doesn't sound like malware, because after a reformat that should have got rid of it, if any malware was there. It could be an issue with over heating.

As a failsafe the system shuts itself down to prevent damage. Hmm?

no. It's not temp shutdown. I said it logged off. It doesn't shut down. There is no reason to your hypothesis, but thanks anyway.

I've installed diff xp now, though and the problems gone. so never.mind