4 Windows PCs. 3 are Win10 and 1 Win7. All 4 have been visible to all others for months. Recently 1 of the Win10 machines no longer lists any of the other 3 under Network in Windows Explorer. The other 3 can see it though. All have Network Discovery and File Sharing on and as I said - working fine for a long time.

The problem PC is connected to a switch via power line ethernet, then to a wi-fi router which is connected to a cable modem. This set up has worked fine for years. 1 of the 3 PCs is connected to the switch via ethernet, the other 2 connect to router via wi-fi.

The problem PC CAN get to the internet.

Further - I can successfully ping the other PCs from the problem PC but still can't see them in Windows Explorer at all. I shut off all network discovery and files sharing on it. Rebooted. Turned all back on, rebooted and still nothing. I have no clue what to try next!?