Reset the router to factory defaults and reconfigure it. If the problem continues, try to replace it under warranty.

As you said, TD-VG3631 is working as a switch, so that DHCP is disabled on its web interface? What's the IP address obtained wireless clients connecting to 3631's Wi-Fi? Can you log in its web...

Can you exit the wizard? Or after finish wizard, can you see the menu on the left side? I'm checking its emulator here. http://www.tp-link.com/resources/simulator/NC200_V1/index.html

I'm afraid not.

I cannot find PA251 on their website anymore. So the problem has not been fixed, right? Did you try to reset them? Power saving is disabled?

*I get weak signal with LAN and WIFI. You are not talking about Wi-Fi signal of WPA4220? Did you refer to speed or something else? What's the rate showing on utility? Have a check pls. WPA4220 is...