If you upgrade it with the right firmware by cable connection and no power cut-off, you can ask for a replacement under warranty.

Except the driver and computer itself, I cannot think up more possible solutions. In your case, Chipmaker's driver may help as I read other similar threads.

Can you access the modem which is connected to WAN port of TP-LINK router? On modem web interface, try to open port 8080 for the router's WAN IP.

It is Faulty.

Since WA7210N is configured as an access point, can you connect to its Wi-Fi and access internet testing by a laptop or phone? What's the hardware version of your W8960N? If possible, use W8960N as...

James, in default settings, wired and wireless clients connecting to W9980 should be able to communicate with each other.Can you ping successfully? Did you Enable Client Isolation or have you done...