I have used this option when I have needed to migrate a SQL server to different hardware and need to restore the MASTER database.
- Open a command prompt
- Type net stop mssqlserver
- Use the cd command to locate your SQL installation ie) mssql\sqldata\binn
- Type sqlservr –m
The server opens in single user mode. When you have finished with the single user mode stop and start the mssqlserver service to start the instance of SQL in normal mode.