[Rob]

Firstly I'd suggest you concentrate on getting the PC to modem connection working properly before you introduce the router.

You've had problems with the NIC drivers, tried updating or otherwise changing those. I suggest you go through your PC (network settings and control panels > device drivers) and delete all the existing setups. Power down the modem, and reboot the PC, with the modem off. Let the PC reload any drivers prompted, and then reboot both PC and modem. There should be no need for any ntl software to be loaded on your PC. Make sure all the new network settings are automatic.

It's worth ensuring your PC is clean of spyware, has current A/V and has a current firewall on, while you connect direct to the modem, although when eventually you connect with the router, if the router has a firewall built in, turn off the PC's software firewall.