System Administrator doesn't work XP

I am logged in on an account that is a "computer administrator". However, when I run the system configuration utility, I am trying to remove programs from the startup, I get a message that, "An Access Denied error was returned while attempting to change a service, You may need to log on using an Administrator account to make specified changes.

Any ideas?

Thanks

Try to open registry editor, group policy editor and task manager. Any similar errors? Either you are not on an administrator account or its a virus doing a DoS attack... :whistling

Try safe mode you can log there clearly to Administrator not try to modify settings there if there is also problem occur then your computer having virus or malware in it so you need to scan your computer with antivirus and every thin is fine then check from there permission of your account