You are putting default SQL port 1433 and instance name which is wrong. Are you sure your named instance of SQL server is running on 1433 port? If you define SQL Server instance name, you don't need to define a port number.
Is firewall port open between Tableau server and your SQL server? You can open the command prompt and try to telnet SQL server with server name and port number you defined.
thiis issue was faced by our user couple of days ago. Installation of dsn entry helped to resolve.
Please work with your server admin to install it.
hope it wilp help