If you designate a network "public" Windows 10 will--correctly in my opinion--tightly constrain what the machine will "see" in that network. File shares won't work, printers can't be seen, and so forth. The only trouble comes if you designate a network as "public" by mistake: there is no easy way to change it to "private"! This seems to be a major oversight on Microsoft's part.
Faced with the problem this morning I found the way to fix it. It involves using the Deep Magic of the powershell, but it worked first time for me. It comes from this page, about half way down.
- Windows-key and search for "power"; you'll get a list of "powershell" options.
- Right click on the simple "powershell" one and select "Run as Administrator".
- In the blue window that comes up, type Get-NetConnectionProfile
- You'll get a list of network connections, each with a number. Select the one you want to change and make a note of its number (let's say it's number 2).
- Now type Set-NetConnectionProfile -InterfaceIndex 2 -NetworkCategory Private, where you replace "2" with whatever your interface is.