Someone posted the following question on itquestions.com, and since the service sucks and wouldn’t allow me to login even after I reset my password, I’m posting the answer here.
I am changing domains on a pc with Vista, i put it in a workgroup, then when i went to log back on, it only gave me the option for the user account, no options to switch to admin. account. I tried booting from ophcrack, but it did not find the user pw, and the admin. and guest accounts said “empty”.
The thing to remember when removing a Windows Vista or Windows 7 PC from a domain is that the local admin account is DISABLED by default. When you switch a PC from a domain to a workgroup, always remember to one of the following before you reboot: a) create a new local account or b) enable the built-in administrator account and set a password.
Since you’re already past that point you can try this trick. Don’t bother trying to crack the open account’s password using 0phcrack or any other dictionary/rainbow table/brute force cracker. You’re just wasting your time. Instead, reset the open account’s password using one of the many free password reset utilities available on the Internet (http://www.rixler.com/windows-password-recovery-bootdisk.htm is one). Most of these tools come in the form of an ISO image you’ll have to burn to a CD. Do that, boot up, and set the password for the open local account to something you can remember.