Windows 10 problem with file explorer, Core and NAS

My Core and NAS (the latter used with ND5XS) are all connected to the same network as is my windows 10 PC.  All has been working OK but today when I open file explorer on my PC, although the NAS and Core both appear, but when I click on either, windows media player opens.  I usually find them in the listing of folders under the network and can open them to view, edit and transfer files.  Now both appear in explorer, under media devices which, when I click on them, opens media player.  Can anyone help please?  I can't find how to correct the settings which have obviously changed.  I can't find a way to make them just appear as folders to open and manage my music.

Thanks to anyone who knows the solution - I'm sure it's a simple change when you know how!