You shouldn't need to do any cloning of MAC addresses to get it to work. Power down the computer the router and the cable modem. Make sure that the Ethernet cable from the Cable Modem is in the WAN port and power on the cable modem, let the modem completely power up and then turn on the router and let it completely power up, then turn on the computer.
Look on the Device status page to see what IP address you are getting from the cable modem, if you are still getting DHCP error, you need to go to SETUP>Network Settings and change the Router IP address in the top box and change your DHCP address Range to match.