Yes the Kindle was turned on and as the builder of Caliber says if you cannot see the Kindle in Explorer then it will never show in Calibre.
I had a Win10 update on Wednesday just past but no change. The weird thing is that the wife's kindle, same model as mine and same firmware but younger by a couple of years shows up on Win 10 on her lappie as does mine. It's annoying and very bizarre.
Latest is I did a factory reset and no change so the only option now seems to be buying a new one. I tried it on the wife's lappie and same same.
PH