Cant log off / switch users on Windows XPpro

So I'm sitting here at this very moment and I cant switch users or log off, I let my nephew use it to play a game on an account I made just for him, but now I need to use the computer and every time I go to log off of his account NOTHING happens when I press the yellow log off button the little screen goes away but nothing else happens after that, its the same for switch users too.
I dont know if shutdown will work either but can anyone explain why this weird thing happened.

8 year olds cant cause this much damage to a computer can they?

>>2
Only with an administrator account, I sure hope >>1 doesn't let strangers (anyone but yourself) use a computer without limiting their user accounts.