4

It should just router after set up pppoe.

Now sure what is the problem. As you said the router itself can access the Internet, then it should just router.

General the problem with modems, is that, when you change router, you need to turn off the modem, change the router, then turn the modem on again. The modem could remember the mac address of the router. But not sure if this is your case. You can just have a try to turn off your modem for 30 seconds and turn on again.