here in ky. when you setup the cable internet service you register 1 mac address to work with the internet service.
ex mac address 00:40:F4:45:CC:XX
if you hook up a router, different computer, or replace a network card in your system the internet stops working. becaues the mac address is not registered with the service. this would be the case I don't know. you will have to call your ISP to register the new device.
what type of service is it static ip adress, dynamic, you will have to configure your service type in the router for it to work properly. most likely its dynamic. to configure the router its most likely one of these
1 option 2
2might check for firmware update for your specific router. check the manufactors web page for these files and instructions
or the blasted router is bad. here recently i have seen alot of bad netgear routers