After you installed your first copy of Windows Vista, how long did it take you to realize that you didn’t know the administrator’s password? With me it was about a week before I needed to make some changes in the file system. It suddenly occurred to me that being logged in as administrator might make the User Account Control dialog box go away, but I didn’t know the administrator’s password! What the heck is the Vista administrator’s default password?

Unlike the previous releases of Windows, Windows Vista does not automatically create an Administrator account during installation. The theory is that the typical Windows user does not need to run with administrator privileges. Using a non-administrator account will prevent a Windows user from accidentally deleting operating system folder, files, and registry information, and prevent any Malware infecting the computer from doing the same. However, if you really need to run as an Administrator, you can easily activate the built-in Administrator account yourself.

Here are the basic steps to activate Vista’s Administrator account and assign it a password:

  1. Logon to Vista using a standard user account
  2. From the Start menu, navigate to the Command Prompt menu item in the Accessories menu
  3. Right-click on the Command Prompt menu item and select Run as Administrator
  4. Click the Continue button on the User Account Control dialog box
  5. At the command prompt, enter net user administrator password, and hit Enter
  6. At the command prompt, enter net user administrator activate:yes, and hit Enter
  7. At the command prompt, enter exit and hit Enter to close the command window
  8. Log off and logon as Administrator using the password you selected

This procedure activates a user account named Administrator and assigns it Full Control security privileges. The user name “Administrator” is reserved, so you cannot create a user account with this name even if you haven’t activated the built-in Administrator account. Depending on the local password policy of the computer, you might be required to enter a password of a minimum length or complexity, and not be allowed to use a blank password.

Credits: James D. Murray
http://www.techexams.net/blogs/jdmurray/what-is-the-windows-vista-administrators-password/