How do you presently login? are you logged into Windows as and Administrator because your PC is setup to log you in automatically
OR are you logging in you PC with a different username who does not have administrator rights?
If you lost your Administrator password and would like to reset your password there are few commercial as well as free utilities you can try the free version first.
Offline NT Password & Registry Editor, Bootdisk / CD - Free
Windows Key - $45
NT Access - $70