@Mannycs 

Modem probably is not recognizing the new router. The modem probably works if you put in an old router if you had one.

To get it to recognize the Deco, leave the Deco wired to the modem and powered on. Only turn off the modem for 5 minutes, then turn it back on.

@Tony 

this worked!!  I wish this was in the instructions.  Thanks so much.  I tried calling and chatting with support but wait times were extremely long

@Mannycs 

I'm having the same problem, but the restart on the modem didn't fix mine. Any other ideas? 

@TexasKellySho 

Make sure you remove any network set ups that failed previously using the TP Link app.  Then restart the install process from the beginning and where mine would fail was when it got to testing the connection.  At that point unplug only your modem for at least 30 seconds and then plug the modem back in.  After about a minute the light on the router turned green and I had a message on the app that the set up was successful.  I verified that by checking one of my wireless TV connections then I proceeded to install the other

@TexasKellySho 

Try the process a couple of times. If a new router still does not get internet, contact your ISP, and say the modem is not recognizing the new router. 

The purpose of rebooting only the modem is so it can forget the router it is currently bound to and recognize a new router. The modem latching to a particular device is known as MAC binding so it registers the MAC address of the connected router and will give the internet to that device.

@Tony Thank you!.  I have Spectrum and was hitting a wall in the initial setup until I tried your solution.

@Tony 

Thank you!  This saved me So much heartburn while setting up my Deco X20!