If you are running the home versions:
- Click on Start button, and type cmd in the Start Search box.
- Right click on the cmd returned on the search results pane above, then select Run as Administrator.
- Type “net user administrator activate:yes”
- Log-off and you should see administrator as an option.
If you are running pro or better:
- Right click on Computer then click on manage.
- Find Local Users and Computers then click on users.
- Right click on Administrator then click on properties.
- Uncheck “Account is disabled”.