Sometime ago I had a similar problem with an SD Card. I had formatted the card in the PC which didn't work. I then formatted it in the Technics Keyboard and it still didn't work because the PC didn't couldn't read the card.
I was advised by Bill Norrie to format the card in the KN Keyboard, save and name the first folder/song. This will enable the PC to recognise the SD Card as 'Technics'.
You can save and use any name you like because it can always be deleted/renamed and the No.1 Folder used again for something you really want to keep.
I suggest you look at Bill Norrie's site where you will find this and other questions answered in detail. It is a very informative site.
Hope this helps.