WN604 cannot connect to router

I have purchased a WN604 access point to provide wireless networking in my home. I have a cable modem (Cisco DPC3825) from my ISP (Mediacom) that works fine as a router/gateware for wired connections.

My plan is to connect the WN604 to my cable modem as a wireless access point (not as a router) so I can use my laptop wirelessly from another room. The problem is that I have configured my WN604 as a DHCP client, but it is not connecting successfully to the network.

What can I do to connect the WN604 to my network so I can use it as a wireless access point?