What's the model number indeed? When internet disconnects, how about status of all lights on powerline devices? Have a check.

As there is no router in your network, how did you share internet with a cable modem? Connect them in the following way and configure WDS on the second C7. Cable Modem((LAN)---(WAN)C7>>>WDS<<<...

What's the model number? Are you looking for Wi-Fi password? If it is a TP-LINK router, there is an instruction. http://www.tp-link.com/en/faq-399.html If you are using a range extender, Wi-Fi...

It is not a common problem. No worries.

Did you try to pair PA4010 and WPA4220? http://www.tp-link.com/en/faq-258.html

Are they still under warranty? Contact your retailer...