Hi There,

Do you have SQL Browser running ? It's needed to direct traffic to not standard ports I.E Not 1433

The fact you can connect when using MSSQL,3456 suggests it's not firewall related

Other thing to try is in SQL Server Config manager go to the protocols for you instance and right click on TCP/IP properties. Wipe out all the Dynamic Ports or TCP Ports in IP1 - 6 so nothing exists in these fields. Then ensure IPALL only specifies TCP Port TCP Dynamic Port should be blank.

Even thou IP1 - 6 are set to not enabled I've seen issues in the past when these fields contain values.

Corinne