SOLVED Computers In Home Network Workgroup Show Inconsistently

[MFL]

We have one home network with most computers connected by cables but one occasionally connects only by wifi. All computers are Windows 10 Home. The modem/router is Comcast's. At no time will all the computers show on their own or the others' network file explorer screen. Their presence or absence changes regularly. Right now my computer shows itself and the two other open computers in its network screen, the second computer shows itself and the third computer on its network screen and the third computer shows itself and the second computer on its network screen. This will change over time as computers are shut down and rebooted. The wifi only computer is not on. I presented this problem here several months ago but none of the many kind suggestions worked.

I was about to replace Comcast's modem/router to see if that would solve the problem because of our good experience with our other home network (#2), which is running on a several months old router connected to the internet by a Charter modem. As soon as I had installed the new router, every computer and device on the network (all connected by cable) started showing up on all the computers all the time...until today. Today, I connected our wifi-only computer to network #2. It did not show all the other computers and devices on its network screen. After I removed it from the network, the other computers became as erratic as the ones in my Comcast based network. So it may not be the routers after all.

Any suggestions?

 

[MFL]

The facts have changed. Our Comcast gateway suddenly died and I replaced it a couple of days ago. At first, all the computers in our all-Windows 10 workgroup showed and were accessible from the network file explorer. After a few hours, one ("Computer A") stopped being accessible even though it shows on the network list of computers. The other computers all remain accessible to each other. The error message we receive when we click on Computer A in the list is the standard "Windows cannot access [\\Computer A] ...etc." I tried \\Computer A directly and got the same message. I can ping it, though. Oddly, Computer A shows under Media Devices in the other computers' network lists, and one can open A's media player from it. Also, another computer in the network has an application which can access a shared folder on Computer A to open files in that folder.

I have tried a lot of online suggestions. None has worked. so I am open to any others. Thanks.