Logout & log in as an administrator

Hello,
My PC have a problem I used window Xp professional. yesterday I was changed my id & password.
than I see today early morning when I start my PC, it was opend with my new id & password but can't
entered me in the system file even not installing software's. every time it's show me error like "You do not sufficient security privileges to uninstall devices or to change device properties or device drivers, loggonin as an administrator and try again" please tell me what I do.