To manage the default database server instance, use these commands:
NET START MSSQLSERVER Starts SQL Server as a service.
NET STOP MSSQLSERVER Stops SQL Server when running as a service.
To manage named instances of SQL Server, use the following commands:
NET START MSSQL$instancename Starts SQL Server as a service, where instancename is the actual name of the database server instance.
NET STOP MSSQL$instancename Stops SQL Server when running as a service, where instancename is the actual name of the database server instance.
Read more at https://technet.microsoft.com/en-us/library/dd421654.aspx
