Adding a Windows user to the local Administrators group will not necessarily give that account full administrative access, as Microsoft has also introduced an additional layer of security called "User Account Control". Some operations are hard-coded to allow the built-in Administrator account access while other accounts will be unable to perform them. 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.