XP Home will not shut down

[Electric Gnome]

I have a Packard Bell with windows xp home installed, it has four user accounts on it, I have no doubt that one of the kids has downloaded some rubbish or registry altering menace, however that will be hard to track.
Before I resort to a complete reformat, or start deleting one programe at a time to establish which program is causing the software conflict, is there a registry tweek that will force windows to shut down. At the moment when you select turn off computer, it goes through, saving your settings, windows is shutting down, then instead of playing dead the little horror re boots.
On one of the accounts though it does in deed shut down, all four accounts are designated administrator accounts.
Any help will be gratefully recieved
mark in the UK

[Electric Gnome]

Silly me, managed to solve this one myself. I had forgotten the simple fix for this as I have never actually seen it enabled before. Entered the BIOS and disabled the "wake on call" facility and bingo no more probs.