HOW TO: Enable the build-in Administrator account in Windows Vista and Windows 7

To enable the build-in Administrator account, follow these steps:
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.