Disconnect the USB connection - you're already connected with your `main` PC so the router can't get a valid IP address to provide internet access (click here). Switch everything off for 5-10 minutes. Hook both machines up to the router with ethernet cables, connect the router WAN port to the modem ethernet port, switch on the modem. Wait until all lights show normal activity, switch on the router. Wait a minute or so (refer to the router manual for `normal` activity indicated by the lights) and switch on one or both PCs. You may need to use the `Create New Connection` wizard on the USB enabled machine to force it to use Ethernet for its internet connection.