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Please confirm that you cannot get a connection, wired, when the ethernet cable successfully plugged in between the modem and laptop, is now unplugged from the laptop and plugged into the router's WAN port, and a new wired ethernet connection is added between the router's LAN port and a PC / laptop. And all devices modem / router / PC have been powered off and back on. I think that's what you are doing but I'm not quite sure?
Your post in one instance says it's a motorola modem, and later you say STB
Presumably you do not have a STB connection.