My little brother gets on one of my laptops running vista and right clicks on my main drive (c and denies me access to it!

I don't have the super user (admin) turned on because I never had a need for it, until now! So I can't chose anything to reverse it, because I am not the admin...

system restore, user account, etc... all "access denied"
even in safe mode!

So, anyone have a solution for this?