>>
>>You are right about the Agent.
>>If SQL Server Express is installed on named instance (which is so) and not use port 1433, how do I find out what port is used? And how to I find out what is blocking user access to the SQL?
>>Thank you.
>
>Ok, I found out (from Task Manager) the port on which SQL Server is listening. But still no solution to what is blocking it. The customer IT says there is no Firewall. But they do have Trend Micro AV but I don't know how to deal with it.

Is the SQL Server Browser service running?