Missing Administrator account

Once you have created regular user accounts, the default Administrator account
vanishes from the Welcome screen, which you see when the computer starts up.
Press Ctrl-Alt-Delete twice at the Welcome screen to retrieve the standard logon
dialog. You can log on as Administrator from here. To switch among accounts, just
click the Log Off button on the Start menu. You'll then see the Log Off Windows
dialog box. Click the Switch User button, and you'll be taken to the Welcome screen
where you can select and log on to other accounts.