Belkin Router works on internal network but no Internet

I recently changed ISPs and my internal server works over wired and wireless connection. However, when I connect an Ethernet cable to my cable modem it does not connect. When I use the ISP provided router in the same port with the same cable it does work. Any ideas on configuration change I may need to make on my router. THE ISP said WAN needs to be dynamic and LAN needs to be static.