Can we just confirm what cables are plugged in where? Should be RJ45 from modem to WAN (Internet) port on Router and RJ45 from one of the four internal ports to the PC. What LED's are lit on the front of the Router and CM?
You can browse to the router admin, but have you tried browsing to the CM admin page (
http://192.168.100.1), and if so does it report a valid IP address?
Have you tried a different RJ45 cable between router and modem?