In the past when I've registered a router with a STB, I've done this:
1. Turn everything off.
2. Connect everything together.
3. Turn on the STB and wait for the light to stablise.
4. Turn on the router and wait for everything to settle down.
5. Turn on a PC (doesn't matter as long as it's connected to the router).
6. Try and visit ANY web page, it should direct you to the provisioning page, otherwise, check that you don't have a proxy specified, try
http://start.ntl,
http://autoreg.autoregister.net and all of the other useful suspects.
7. Create a name for the Router, once the new profile has been created, turn everything off once more, repeat steps 1-5 and you SHOULD have a working Internet connection.