You cannot log on after you remove the computer from the domain

After you change a computer's membership from a domain to a workgroup and restart the computer, you cannot log on with your previous user name and password. You may also receive the following error message:

This behavior occurs because the user name and password that you previously used are available for logon only to a domain. Your computer is no longer a member of a domain. Therefore, your logon attempt must be validated on the local computer by using the local security database. To log on to the computer, you must provide a user name and password that exists in the local computer's user database, or Security Accounts Manager (SAM).

To avoid this behavior, make sure that the local security database on the computer contains the default Administrator account from when the computer was first installed, together with any additional user accounts that have been created, in its local users security settings.

If you do not know the local user account and password, you cannot log on to the computer. To resolve this issue, use one of the following methods, as appropriate for your operating system.

For Microsoft Windows NT 4.0

Use a recent copy of the Microsoft Windows NT Emergency Repair Disk (ERD) to restore the registry files on the system. This resolution lets you restore the computer's user database (or SAM) to a version for which you have a correct user name and password.

Be aware that when you replace the SAM from the ERD, this replaces the user accounts and passwords with those that existed on the date that the ERD was created. Therefore, when you use an account that was created by using this method, you have to know that account's password on the date that the ERD was created.

Also, depending on the options that were used when the ERD was created (such as whether the /S switch was used or not), the ERD may not include all existing user accounts.

By using the ERD, you are also required to start your computer from either the Windows NT 4.0 CD-ROM or from a boot disk, and to select the Repair option. During the repair process, select only the Registry option in the first window. Later in the repair process, a second window will offer options for which registry hives to repair. Select the SAM option.

For Windows XP or for Windows Vista

Use a System Restore Point to restore the computer to the time at which the computer was added to the domain. Then, log on to the domain. Make sure that you know the user name and the password for an account in the local Administrators group. For more information, see the following Microsoft Knowledge Base article:
For more information about ERDs and how to perform an emergency repair in Windows NT, click the following article numbers to view the articles in the Microsoft Knowledge Base:

If you do not have an ERD, you can work around the issue by installing a parallel installation of Microsoft Windows XP, Microsoft Windows 2000, or Windows NT. A parallel installation lets you log on to the computer. Therefore, you can gain access to the computer or copy files from it. However, this method will not let you retrieve either user names or passwords from the original Windows XP, Windows 2000, or Windows NT installation. Therefore, it is better for you to know a user name and password for a member of the local Administrators group before you change a computer's membership from a domain to a workgroup. After you have backed up all the files by using the parallel installation, you can reformat the hard disk and then reinstall Windows XP, Windows 2000, or Windows NT. Or, you can configure the new parallel installation for your needs and use it instead.

For more information about how to perform a Windows NT parallel installation, click the following article number to view the article in the Microsoft Knowledge Base: