|don't understand this question. vista has built in Administrator account, which is disabled by default. so what's this about renaming yourself as administrator? (you can't rename a 'normal' account to administrator).|
What I'd do with a second hand machine is create a new user for myself which would be member of administrator's group. Then I'd remove any previous create user accounts & their associated files, so only my user is available to log on with. It sounds to me that you may have renamed the previous user account, but that doesn't renames its user profile.