The built-in administrator account is disabled by default in Windows Vista on new installations.Microsoft has hidden the Administrator account in Vista, but it’s easy to resurrect once you know how to find it.
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”
Now type the following command
net user administrator /active:yes
You should see a message that the command completed successfully. Now log off, log on with the new administrator account. Here you go. After 1st logon, rename the new admin account to whatever you like. Assign a new password and delete your install account.
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.