Just to add my two pence to this thread....
I had similar problem with my kindle 6th gen after upgrading to Win10.
My laptop recognised that something was attached (ie my kindle) but would not let me open it in explorer to manually transfer books. Calibre also could not recognise it meaning i could not transfer books manually using calibre.
Solution was to 1: open device manager 2:attach my kindle 3: uninstall the 'usb mass storage device' which then appeared in universal serial bus controller (in device manager) 4: disconnect the kindle 5:restart laptop and kindle 6: reattach kindle after both have fully restarted (laptop now recognised kindle in explorer) 7: start calibre which should now (hopefully) also recognise the kindle.
All this means i can finally manually transfer ebooks once again
and return to being a
