switch user causes reboot

I have 3 user accounts on WinXp SP1. A few weeks ago, my machine started just rebooting when trying to switch between users. For the life of me, I cant remember installing anything new or doing anything different.

Basically using the Windows key and "L" causes the machine to reboot.

If I choose start - log off - switch users, then try to either go back into the same account, or go into a different account, the screen flashes to blank black, then back to the log in window with the 3 user accounts listed. there's then no way to go back into any accounts, without rebooting the machine.

any ideas/clues?
thanks.

 

Any errors in the event log generated when you try to login, but cannot?

Any VPN software for you to connect back to work?

 

Try Creating 3 more new users

 

have given up on this issue. PC is starting to play up with all sorts of things, so time for a format/rebuild.

Cheers.

 

I think that should sort it out good luck