How to make a new admin account on windows 7 with a limited account?

I need to make a new administrator because one of my room mates thought it would be funny to make himself an admin and me a limited account user. I would be OK with this but i had put time restrictions restricting all access to his account. Now every time i try and use his password to make a new admin to fix this i get a error message saying that there are time restrictions. Any help would be appreciated.