@USNGreenie,

First things first, try rebooting your modem without anything connected to the modem and wait a few minutes. Try then setting up the Deco. This will allow your modem to reset its connection settings and may help to fix any problems with the handshake between your modem and router.

For Your Deco, any of the ports will be able to connect to your modem, however, it is likely that your modem will only provide a connection through one of the ports.

You may also try to perform a MAC Clone for your deco if you are continuing to have issues establishing a connection, the steps to do so can be found here: Performing a MAC Clone on Deco

Do you know if you have a gateway or a modem? If you have a gateway that provides its own internet connection, you should try and enable Bridge Mode or IP Passthrough Mode on your Gateway.