How to enable the Administrator Account on Windows 7 or Vista from User login if you know Administrator Password

Enable Built-in Administrator Account

First you’ll need to open a command prompt in administrator mode by right-clicking and choosing “Run as administrator” (or use the Ctrl+Shift+Enter shortcut from the search box)

Now type the following command:

net user administrator /active:yes

You should see a message that the command completed successfully. Log out, and you’ll now see the Administrator account as a choice.

Log off the system and login again

Done.