Follow Johns instructions - but try rebooting the hub (it should stay in modem mode) with the router connected - let it boot back up and see if you have an internet connection - and that the router has acquired a WAN side IP address.
It can be troublesome - I had to do a reboot (power off/on) of the hub modem to trigger the Virgin DHCP server when I connected my own router recently. It sat for like 30 mins saying no Internet (and had no WAN IP address) but got one straight away when hub was rebooted.
You can also connect a laptop direct by ethernet cable and see if you have web access.
------------------------------------------------------------------------------------------------------------------------------
I know a bit about Wi-Fi, Telecoms, and TV as I used to do it for a living but I'm not perfect so don't beat me up... If you make things you make mistakes!