Adding a Windows user to the local Administrators group will not necessarily give that account full administrative access, as Microsoft also introduced an additional layer of security called "User Account Control". If you know what you're doing and want to disable it:
Open a command prompt with the "as administrator" option and run
Computer Configuration ->
Windows Settings ->
Security Settings ->
Local Policies ->
User Account Control: Run all administrators in Admin Approval Mode and select "Disabled".
Restart Windows and you should have your permissions resolved.