Enable the (Hidden) Administrator Account on Windows 7 or Vista
Many people familiar with prior versions of Windows are curious what happened to the built-in Administrator account that was always created by default. Does this account still exist, and how can you access it?
The account is created in Windows 7 or Vista, but since it’s not enabled you can’t use it. If you are troubleshooting something that needs to run as administrator, you can enable it with a simple command.
Note: You really shouldn’t use this account for anything other than troubleshooting. In fact, you probably shouldn’t use it at all.
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.

You’ll note that there’s no password for this account, so if you want to leave it enabled you should change the password.
Disable Built-in Administrator Account
Make sure you are logged on as your regular user account, and then open an administrator mode command prompt as above. Type the following command:
net user administrator /active:no

The administrator account will now be disabled, and shouldn’t show up on the login screen anymore.