Open a command prompt in administrator mode by right-clicking and choosing "Run as administrator"
Enable the hidden administrator account
net user administrator /active:yes
Disable the hidden administrator account
net user administrator /active:no
Adminstrator account has no password so you will have to go to user accounts in control panel and set on up if you want to.
For more details and pics visit the How to Geek:
http://www.howtogeek.com/howto/windows-vista/enable-the-hidden-administrator-account-on-windows-vista/
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