You may run across the situation where SQL has been locked down to the “sa” user and the password was lost/forgotten. In this situation you can start SQL in single user mode which allows you to connect with Windows authentication again.
1. Open the Configuration Manager tool from the “SQL Server 2005| Configuration” menu
2. Stop the SQL Server Instance you need to recover
3. Right click the MSSQL Server instance and choose properties
4. Navigate to the “Advanced” tab, and add “;–m” to the end of the list in the “Startup parameters” option
* NOTE: make sure there is no space between “;” and “-m”, the registry parameter parser is sensitive to such typos. You should see an entry in the SQL Server ERRORLOG file that says “SQL Server started in single-user mode.”
5. Click the “OK” button and restart the SQL Server Instance
6. You will now be able to access SQL using Windows authentication to reset the “sa” user’s password.
7. Finally Remove the “;-m” from the startup parameters using the Configuration Manager and restart SQL