The master Administrator account is not visible by default in Windows 7 or Vista.
However there is a simple way to enable it.
This account has complete access and permissions on the computer.
The simple steps to enable and disable the master Administrator account in Windows 7 are as follows:
Enable Administrator Account
  1. Open the command prompt in administrator mode
    1. Type ‘cmd’ in the start menu search box:

    2. Right click on the Program ‘cmd’
    3. Select “Run as administrator”:

  2. In Command Prompt:
    1. Type in the command ‘net user administrator /active:yes’

    2. And you are done !
    3. Logoff and login again and you will now see an option for Administrator login!

    4. Note: It is advisable to create a strong password for this account.
Disable Administrator Account
  1. Login with your current user account.
  2. Open the command prompt as per instructions provided in Enable Administrator Account, Step 1 (above).
  3. Type in the command ‘net user administrator /active:no’

  4. And you are done!