Update: I bought a new router (it's linksys) and I'm having the same issue. So maybe it's the modem. The instruction manual for the modem only says plus in an ether net cable, coax cable and the power cord....it's kinda useless. I haven't been able to find any other threads experiencing a similar problem so maybe it is just the modem...it just doesn't make sense that it would work Fromm the modem directly to my computer but not through at least 1 of 2 routers....
9th post down has some good ideas to try,only other option unless getting a same make router for whichever device manufacturer is to use a network switch http://www.techrepublic.com/forums/discussions/cable-modem-and-netgear-wireless-router-not-routing/ just had a thought do you have a spare pci network card & perhaps bridge it & then connect router to that instead (assuming you have a desktop somewhere your connecting)
This is going to sound really dumb..... Originally, I tried unplugging everything and turning them both on at the same time and then reconnecting.....What I had to do was disconnect everything and then start up just the modem with the coax and power, no ethernet attached. Once it initialized, I connected the ethernet from the modem to the router and I was good to go. I don't understand why it didn't work turning them both on at the same time.....but at least it's good now.
Right.. down the rabbit hole we go.. this nonsense is being caused because the router is issuing dhcp addresses.. and no doubt the isp modem wants to do that job itself.. in the settings for both look for "dhcp" and turn one of them off.. your fix is the clue.. both were trying to issue an address to the wire between them.. and conflicting.. having the dhcp up on one then powering the other meant it got it's address from the running dhcp server and didn't then try itself
you know,come to think of it i had to do this when i set up another router as a wireless access point.this is why we love you ps.