Thanks guys, but unfortunately it still doesn't work. I know that the leads I'm using work fine, and I've tried cloning the MAC address. Firstly, I don't think I should need to do this as you don't have to 'register' with Virgin broardband like I had to with NLT, and secondly, you need to put a hostname in along with the MAC address - which I don't have with Virgin anyway.
I've done numerous factory resets, but still no joy. My computer happily talks to the router, but my router does not want to acknowledge my modem.
Any more ideas, it's driving me mad?