Consulte Windows 7 - Conta de administrador interna - Ativar ou Desative para mais informações.
Veja a OPÇÃO ONE neste site.
Through Local Users and Groups
NOTE: This option will only be available in the Windows 7 Professional, Ultimate, and Enterprise editions.
Open the Local Users and Groups manager.
In the left pane, click on the Users folder.
In the middle pane, right click on Administrator and click on Properties.
To Enable the Buit-in Administrator Account
A) Uncheck the Account is disabled box.
B) Go to step 6.To Disable the Buit-in Administrator Account
A) Check the Account is disabled box.Click on OK.
Close the Local Users and Groups window.
Log off, and you will now see the built-in Administrator account log on icon added (enabled) or removed (disabled) from the log on screen.
NOTE: Click on the Administrator icon to log on to the built-in Administrator account.