WRT1900AC and BT Infinity

Please may I ask for some assistance.

I have bought the WRT1900AC to replace my BT Homehub 5. On the box it states (on a sticker) suitable for BT Infinity.

So, I unplugged the Homehub 5, plugged the same cable (2pins on each end) to the WRT1900AC and let teh LinkSys do its thing...which was, nothing. It ran through the automatic configuration and said 'no internet detected', click 'Next', so I did, and again and again.

Has anyone used the WRT1900AC to replace a Homehub? how do I do it, am I being stupid? I know little of these things but need some help!

Thanks to all.