Acer aspire 2920 webcam won't work in msn messenger

i have an Acer aspire 2920 which has built in vista, and also has a built-in webcam. I use a standard account, while my dad controls my account via the admin account.

The webcam is crystal eye, and whenever i try to webcam with my friends the same message comes up which says something like, "your camera appears to be in use in another application please close them and try again." and i don't know what to do because i tried closing everything else, but nothing happened...

Please help?

Thanks,
Anna