Enable or Disable administrator account in Vista using command prompt

1. Click Start, and then type cmd in the Start Search box.
2. In the search results list, right-click Command Prompt, and then click Run as Administrator.

3. When you are prompted by User Account Control, click Continue.
4. At the command prompt, type net user administrator /active:yes, and then press ENTER. 
5. Type net user administrator , and then press ENTER.
Note: Please replace the tag with your passwords which you want to set to administrator account.
6. Type exit, and then press ENTER.
7. Log off the current user account.
To disable the admin account repeat the above procedure again type the command net user administrator /active:no in step 4