@decodave 

Hi, how about the LED light on the main Deco? is it solid red or green?

"There's no blinking light by the ethernet cable on the X55. The same ethernet cable out of the modem still blinking." There hasn't been any Ethernet port on Deco. May I know which light you refer to?

Have you tried to unplug Deco and connect to a laptop to see whether the internet works?

It is also suggested to refer to this link:

Unable to connect to the Internet

Thank you very much and best regards.