Help with administraive rights

my system is vista. i am using an administrator account but i am unable to access everything that requires to run as administrator. running files like regedit gives an error of
“Windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item”
for trying to turn UAC off, no error is given but it would not let me access.
my system also has trustedinstaller so its like i cannot access everything which requires administrator permittions.
help please. thanks

Even if you run regedit as “C:\Windows\System32\regedit.exe”?