[MovedGoalPosts]

yes, turn off the power to modem, router and computer(s). Plug in your new ethernet connections to the router (old cable connections from the ethernet / USB to PC are disconected). Power on modem, let settle, power on router, let settle, power on PC.

The modem will not recognise that whatever is directly connected to it has changed, and thus doesn't speak to it, unless it is repowered.