you have to turn the computer/xbox & modem off, plug the modem into the rj45 socket, then turn on the modem, let the lights settle (about 20-30 seconds), then turn on the computer/xbox & let it boot normally - you should get a connection.
- you have to 'power cycle' the modem every time you change the device plugged into it
- dunno about the V3 router, though, sorry..