As you are using Express DB so that machine might be not using dynamic port.Try JDBC url with the below format.
jdbc:sqlserver://host;instanceName=instance;databaseName=database
Here Host:IP address or Hostname
Instance Name :By default it is MSSQLSERVER.
Database Name:Your db name.
We use this URL if we are not sure about Port no of sql server so we provide instance name.
I hope it will help you.