Have you tried re-booting the Cable Modem?
Turn the modem, router and PC off.
Turn the Modem back on and let it power up and settle down.
Turn the router back on, let it power up and settle.
Now turn your PC back on.
What happens?
If that doesn't work have you tried taking the router out of the equation completely, plug the Cable Modem directly into your PC. Do you get a connection then?
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to CF by the way