To stop and start SQL Server services using SQLCMD mode, open a new query window and change the query execution mode to SQLCMD:
Click 'Query' -> 'SQLCMD Mode':
You can also execute the commands from SQLCMD.EXE utility (usualy can be found in C:\Program Files\Microsoft SQL Server\110\Tools\Binn but path may be different depending of the version of SQL Server you are running and installation location).
To stop SQL Server Agent and SQL Server services, execute following SQLCMD commands:
!!NET STOP SQLSERVERAGENT
!!NET STOP MSSQLSERVER
To Start SQL Server and SQL Server Agent services, execute following SQLCMD commands:
!!NET START MSSQLSERVER
!!NET START SQLSERVERAGENT
To start or stop a service of a named instance, replace MSSQLSERVER with the instance name.
You can start or stop other SQL Server services like SQL Server Browser, Integration Services, Analysis Services, Reporting Services, using SQLCMD command and the correct service name: