My development machine was rebooted after a windows update recently and now I can't access my admin account.

I never reboot my machine except when forced by WU so I actually don't know if the problem is related to WU. Don't remember when I last used the admin account but it is probably a week or 2 ago.

Normally I run in a normal user account and keep an admin command prompt open to deal with admin tasks.

What happens now is:

  • If I do something that triggers the UAC and enter user ".\admin" and password I get the message
    Logon failure: unknown user or bad password

  • If I do RUNAS /user:.\admin cmd I get the message
    RUNAS ERROR: Unable to acquire user password

Any idea what the problem is?

It is not a big problem since I can call in a domain admin but I am curious about what has happened and why UAC and RUNAS show different error messages.

1 Answer 1


The SAM file might have been damaged. Explanation on [SAM]: Where are Windows 7 Passwords Stored? is available here.

  • 2
    There were no error messages or event logs about corrupt SAM file but problem was solved by resetting the admin password. Strange it can happen like this. What would I do if I didn't have the domain administrator?
    – adrianm
    Sep 25, 2013 at 9:11

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