[Rob]

Can you confirm you are using cable rather than ADSL, and the router is cable compatible, i.e. it does not have an inbuilt ADSL modem, and the WAN (internet) port is ethernet? If in doubt post the full make / model of the router.

Some users have had issues with the ethernet cable between modem and router. Might be worth swapping it? Remember to power off the modem every time you swap the cable or device directly connected to it.