@djsegler 

Hello. With computer connected to the Deco M4 by wired cable, please verify whether you can get internet and please click here to verify the IP address and gateway. 

In the meantime, please connect computer to the modem directly, bypass the Deco M4 and test whether you can get internet; if not, then Deco won't work either and you can give a call to ISP to get some help; If it works, you can reboot the whole system, including modem and Deco units. 

Still the same, you can reset and reconfigure Deco M4 to give it a go.

May it help.