System Restore

Ok I am really screwed up. some guy hid my admin account using the registry
hack. (add a dword with the account name) and now i cant log into anything
but guest. When trying system restore i got:

there was an unexpected error

class not registered

Please close system restore and try again.

Is there any way I can fix my main problem which is to unhide my admin
account? All i can do is remove the password on it. I just need to log in and
delete the registry key or use system restore, which doesnt work.

Need help
thanks.