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When you say broadband box can I assume this is a Cable Modem?
Are you powering off the modem, then unplugging from the modem the lead that served the USB, then plugging in the ethernet lead to the router, and only then powering up in sequence the modem then router then PC (lappy)?
Have you tried connecting the lappy direct by ethernet to the modem (remember the modem must be powered off whenever the device directly connected to it is swapped over).