[Paul K]

Ok what have you done so far? Basically you connect the modem output to the WAN port on the router and then connect everything else to the router itself.
One thing to do is power off everything before changing any physical connections to the modem, once the connections are changed over power up the modem, wait for the lights to lock/ settle, power up the router, wait for lights to lock/ settle and then power up the PCs. At this point open a browser on the pcs connecting to the router and see if you can access the router settings page, if you can then all should be well as long as the modem is "talking" to the router. If you cannot access the router page then something is wrong between PC and router.