The easiest way to enable or disable the administrator account is from the command line. Open a command prompt with administrator rights. This is done by right-clicking on the command prompt icon in the Windows 7 start menu and selecting Run As Administrator from the available options.
Then in the command line to enable administrator account using the following command:
net user administrator /active:yes
To disable the administrator account using the following command:
net user administrator /active:no
To change the password of administrator using the following command:
net user administrator *
Another mothed is to go to Control Panel —> Administrative Tools–>right click Local Security Policy and select “Run as administrator”
Then find the option under Local Policies-> Security Options ,then double click “Accounts: Administrator account status“.
Note:To enable/disable the built-in administrator account,you must have the administrator privilege.