Administrator in XP doesn’t work

I just installed WIN XP Pro with 2 user accounts on a clean hard drive. My account shows as administrator but I can’t make any changes as an administrator. Specifically, I’ve tried to shut down some startup items in msconfig and change the radio button from selective startup to normal startup. It keeps telling me I have to have administrtive privilages. The only thing I’ve done different is that now I’m using Nortons virus.
thanks,
gweb