What model router is it?
What have you tried doing so far?
Expanding on homealone's very relevant question above.... If you use a standalone cable modem (SACM), you need to reboot the modem before 1st connecting the router (see here:
http://homepage.ntlworld.com/robin.d...tips/swap.html). If you use a digital TV set-top box (STB) for broadband, then you have to either register the router's WAN port's MAC address (see
http://homepage.ntlworld.com/robin.d...r.html#pacereg ) or clone the PC's MAC address onto the router.