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Firstly you must power off the cable modem when swappiing over the device directly connected to it, be that a computer or router. The modem will only speak to a single device so you cannot have a USB and ethernet lead connected at the same time.
Try powering everything off, computer, router modem. Plug in ethernet from modem to the router WAN port, ethernet between router LAN and computer. Power on modem, allow to settle, power on router allow to settle, power on PC.
Computer network settings need to be on autodetect.
You aren't trying to use an ADSL based router are you ?