I just bought this Archer C20 v5 wireless router to set up as a wireless router with my modem. Internet keeps dropping from all devices even though router and modem lights remain on and connected. 

First, no ISP issues. Internet connects and stable when PC is wired to modem.

Second, all internet activity has been web browsing and video streaming only. 

Scene 1: When router has wifi disabled and is wired only to my PC, internet is stable for several hours but will disconnect: 1. Eventually after several hours and/or 2.  if I attempt to wire a second device through LAN port on the router.

Scene 2: When router has wifi enabled and the PC alone is connected through ethernet, it will work possibly without interruption. BUT if other devices connect wirelessly, all wired and wireless devices will lose internet at the same time. Duration of internet connection on all devices after wireless devices join the network varies from 2 seconds to 30 minutes. 

I have dynamic IP address settings.

DHCP router settings are set to automatic.

I tried both cloning and not cloning MAC address. 

All this was attempted before I upgraded to the latest firmware but I really don't think that will resolve the issue. 

I think the issue has something to do with DNS or DHCP router settings but I don't understand how all this works. 

Please help me. I'm stupid and have to work from home.