Try to login in build-in administrator account and make diagnose &
repair.If there is no any administrator account build-in admin should
appear in safe mode -if not you have to enable build-in admin remotely

There are many various methods to do that:

link I:'What do I do: I can no longer log in or elevate to an
administrator account' (http://www.jimmah.com/vista/content.aspx?id=7)
link
II:http://www.vistax64.com/tutorials/20...ge-win-re.html

apart of above methods alsoTools for reseting password also have option
to enable/disable accounts (for built-in admin also) for example
'Offline NT Password & Registry Editor'
(http://home.eunet.no/pnordahl/ntpasswd/)


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Flavius