2 week old Archer A20 router. occasional problem with connecting wired computers to the router. They don't see the router at all or recognize a connection. 

Works fine for a while then problems arise. Can connect mobile devices via wifi and get good internet connection.  

Can direct wire desk set to the modem and get good internet connection using the same ehternet cable that I use for the router connection so etherniet cable is good.  When wired to the router it acts like it is not connected.  3 computers hard wired to the router and none are connecting now. 2 are Win10 Pro and one is Win 7,  

Feeling frustrated, wired connections should be simple.  

What am I doing wrong?