Netgear router not recognizing internet from modem?

my netgear router suddenly does not recognize the ethernet cable coming from my comcast modem. i can connect the ethernet directly into the back of the computer and it glows green just like it does on the other end thats connected to the modem and i have internet. Normally, when the ethernet cable is plugged into the router from the modem it glows green in the modem end as well. now it no longer glows green so ive deduced its a problem with my modem. so my question is how can i get my netgear router to recognize the internet coming from the modem? i know how to change the router settings with the adress on the back of the router but im not sure if those settings will solve the problem.