XP Pro SP1 had been running fine with just the Administrator account, and one other account with administrator priviliges.
When I added a new user with the wizard, limited account, XP makes it to desktop with that account and then reboots.
The same happens with the guest account.
Previous accounts with admin rights still operate fine.

I created a new user account with administrator rights, logged onto it, and all was fine.
Logged off it, changed priviliges to limited, and when I logged back onto it, XP rebooted again.

Any help as to why I cannot create a new user account with limited access would be appreciated.
As I said, the original Admin account and user account both work fine through all of this.