How do I regain Admin privileges?

I left on vacation over the past weekend. Upon my arrival home, I went to my computer to check my mail. I noticed a second account but thought nothing of it on the log-in screen. Later, as I am trying to update my programs such as iTunes, I come to find out that my administrator privileges are gone. My roommate has confessed to changing adding an administrator account and demoting my account. However, the password he set was from a random password generator and is only recorded in a text file on the desktop of the admin account. How do I regain my administrative privileges on the computer and delete the other account?

I have an HP Pavillion p7-1207c.
I have tried restoring the system from a backup, but that requires an admin's permission.
All help is gladly accepted.

Use the method given by Kaktussof, provided you have a W7 disc.

If you don't have the install or repair disc, take a look at Offline Windows Password & Registry Editor, you will need to downloiad and burn the .iso to a CD.

Be sure to break a few of your room mate's fingers!

Thank you so much! I wrote the iso to the disk, played around with the settings a bit, and voila! I didn't hurt my room mate.... I just got $200 out of him :P

I'm glad everything worked out for you!

By the way, welcome to Sevenforums!