Start SQL Server Instance in Single User Mode

To start SQL Server instance in Single User Mode, follow this simple procedure:

1. Stop all SQL Server related services (some SQL services such as SQL Agent will use up your only connection in single-user mode).

2. Start the SQL service with the -m parameter.
In SQL Server Configuration Manager, click SQL Server Services. In the right pane, right-click SQL Server (), and then click Properties. On the Startup Parameters tab, add -m; parameter (do not add a space between the -m; and the rest of the command line).

Or from CMD with 'Run as administrator' input:

NET START MSSQLSERVER /m

This will put the SQL into Single User Mode, and SQL Server will only accept one connection.

If you get the error message:

Login failed for user 'domain\username'. Reason: Server is in single user mode. Only one administrator can connect at this time.

It means that there is something using your single connection. You need to find the service or connection that uses up the only connection and stop it before you can log in. Check SQL Agent, SQL Reporting Services, SQL Analysis Services...