Why is my router not receiving DCHP settings from my cable modem?

I have a Motorola SB6120 cable modem and a Linksys router. The router is configured to obtain its IP settings via DHCP. I have been using this configuration for at least a year now with this equipment. Suddenly my router no longer receives settings via DHCP. I connected a laptop directly to the modem and it received IP settings via DHCP. I then connected a new Cisco router to the modem and it is doing the samething the Linksys was doing, no IP. I replaced the Ethernet cable connecting the two pieces of equipment. That did not fix it.