It sounds like the router is the problem. It should have an instruction which tells it how to translate the IP address from external to internal, and it sounds like that's not happening.

Can you ping other devices through the router? For example, an internal laptop to/from an external laptop? Do you have the appropriate ports open on your router (2000, for example, telnet port, etc.)? Services permitted, including ICMP (to permit pinging), Telnet, SecureTelnet?