Please check that you have the correct SQL server name and if required the proper instace name for the SQL server you are trying to use.
To find the instance name open Services on the SQL server.
Look for the following.
SQL Server (MSSQLSERVER) - this is a default of instace of SQL. To conncet to this you only need to specify the SQL server name.
If it is a named instance it will look like the following.
SQL Server (LYNC10)
In this example to connect to this SQL server and instance I would type in - <SQLSERVERNAME>\LYNC10
