OK, it is listening for connections on any interface.

From your server can your client connect to 127.0.0.1 on port 1234?
No: The client or server code is faulty
Yes: Carry on

From a machine on your LAN other than the server can your client connect to server's LAN IP address?
No: The problem is quite probably your server's own firewall. Windows firewall or anti-virus perhaps?
Yes: Carry on

Install Wireshark or a similar tool on your server machine. Start a capture. For a machine outside your network can your client connect to the server?
Yes: Problem solved
No: Carry on

Did you see the attempt to connect to port 1234 in Wireshark?
No: Problem is the firewall or port forwarding from your external connection.
Yes: Problem may still be a firewall on the server itself if it restricts by source IP address.