Does your web browser ask you to remember the password?

Any other devices are connected to C7 directly and access internet? When the router stops working, can you login its web interface? How about status of all lights like system light on its front...

I didn't realize that you have no powerline extender... Units in PA4015PKIT have no Wi-Fi function. To access internet, you have to connect it by wire. Password in screenshots you provided can be...

Check anti-virus software and firewall settings on your clients. Wired devices can communicate with each other and wireless devices can communicate with each other as well? BTW, firmware of your C7...

You mean D5? That can work as an ADSL modem router, while C5 is a wireless router.

I don't understand what you are trying to say and expect... How do you want to access internet by W8960N?