On some installations, we've experienced the need to create exceptions in Windows Firewall for Microsoft SQL Server and SQL Browser to allow the server to accept incoming connection attempts from the clients.
Go to Windows Control panel and access the Firewall settings. Click on the "Allow an app or feature through Windows Firewall":
Then, click on the "Change settings" button:
Then the "Allow another app":
Click the "Browse" button and then navigate to you SQL Server installation path. I.e:
C:\Program Files\Microsoft SQL Server\MSSQL13.SQL2014\MSSQL\Binn\
Here, choose the file called sqlservr.exe and add it. The navigate to:
C:\Program Files (x86)\Microsoft SQL Server\90\Shared\ and add the file called sqlbrowser.exe
When both files have been added, remember to tick on the required firewall exception:
When finished, test the connection between the clients and the database.
For more information from Microsoft please see the following link: