[Rob]

Very odd, if the ethernet works when connected direct between modem and PC, there is no reason why it shouldn't work when connected between modem and router WAN port. You are power cycling the modem every time to change over the connection?

It should be a straight through, not crossover cable. I'd suggest you try a different one, just in case, but you've probably been there already.

A suggestion I've seen elsewhere is to power off the modem for a lengthy period of time, say overnight, along with the stuff connected to it. When you power up do so over a few minutes, i.e. modem first, couple of minutes later router, and the later the PC. I have no idea why this should work, but the poster swore by it.

You have purchased a router with wireless access point, rather than just an wireless access point?