Msconfig error-can’t make changes although I am the administrator

When I try to make changes in MSCONFIG, I get an error that says..I must be the Administrator
to make changes. I am the adminstrator and the only user of my computer. I need to remove some programs from the MSCONFIG so how do I tell my computer that I am the administrator or why doesn’t it know when I start my computer? How do I know that when I start my computer that I am being logged on as the Administrator? When I do logon I am logged in as a User who is the administrator when I check the users file but in Msconfig I am not
recognized as the Administrator!
My OS is Windows XP Media Center SP-2.

Thanks for your help!
DVancenza