I found the answer.
You have to use the Command Prompt
Start --> Accessories --> Right click on Command Prompt -- Run As Administrator
Then type the following string which meets your needs:
To enable the Windows 7 administrator account:
net user administrator /active:yes
To disable the Windows 7 administrator account:
net user administrator /active:no
To change the password of the Windows 7 administrator account:
Net user administrator password
