The built-in Administrator account is not enabled by default in Windows 7 and Vista. To enable the Administrator account, you need to perform the following steps:
Click Start and type ‘CMD‘ in the search bar. Right click CMD and select the option Run as Administrator.
Type the following into CMD:
net user administrator /active:yes
The message below should state that the command was completed successfully.
Note: To disable the Administrator account type the following into CMD:
net user administrator /active:no
Exit CMD. Log out of Windows and you will see the Administrator account is now available at Start up. The example below is taken from Windows 7 Ultimate.