When you try to view the card contents on the player using the folders menu, do you see all the songs on the card, or just some of them? If the player shows many songs on the card, what happens if you try to play them?
I’m trying to figure out what is going on, however you give so little information, so it is hard to figure out what is going on. I had two Fuze players a few years ago, but no longer have them.
If you have copies of all the songs on the card also on your pc, I suggest that you set the USB mode on the player to MTP, connect the player to your pc, and delete all the files you see on the card. Disconnect the player, change the USB mode to MSC. I found that having any MTP transferred files on card memory caused strange problems.