I am having problem with my Windows Vista Home premium edition.
I am logging with Administrator account but still is not giving me excess to all the right which administrator has. If I am opening my c drive it is giving error "access is denied". Also if am doing any changes to user accounts it is giving error "cannot open access control editor" and "access is denied".
When going to properties of c drive it is showing unknows owner in ownership tab and dening access to administrator to do change ownership to the default user.

Initially I was using my default user with admin right, but when i started getting problems, I have activated Administrator user. And now very much surprise that how my administrator account is behaving like a normal user account.

Can any one help me the same?

I think You should have to Open certain thing in compactibility mode (XP or 98) through properties but if the problem still alive then it is better to form a new user wth admnistrator even this fails it is better to format and load a good anti virus!

Turn off User Account Control.
Start>Control Panel>User Accounts>Turn User Account Control on or off