SQL connections can be a bit finicky & can get complicated by name resolution, authentication and other things such as the configuration of the SQL server.
Is that SQL server a remote machine (or local)
If local, you could try localhost or 127.0.0.1
If remote- try the IP address
I have used the Slingshot package successful- give that a try & search for my name & slingshot on this forum.
This one might help Creating MSSQL DB Connection
Try creating an ODBC connection (which you can test using other applications) and then use that connection instead of the server details
Andrew