[MovedGoalPosts]

OK, working solely with the master PC and it's Realtek card, and the modem. Nothing else connected to the modem or PC and just one straight through ethernet cable.

Turn off all firewalls, andtivirus and the like (we can turn them back on later once we prove there is a connection.

Ensure the realtek card is enabled (check network connections), and has the latest drivers loaded. Check in Control panel that there are no other network devices ghosting around.

Delete any old USB network drivers (warning you may not be able to get back online via USB once you've done that).

Make sure the Network card properties are set to automatically receive an IP address.

Make sure your internet explorer settings are also set to automatically detect (Tools > Options).

When you are wired up, are the lights on the modem and network card lit? If they don't light try a different cable.

Make sure you are rebooting the modem and PC whenever you disconnect whatever setup you have been posting to this thread with and connect up the PC network card to the modem. The modem will not detect that the connected devices have changed with out it being powered off and back on again.