I did see your original post and wrongly assumed you had sorted it. Without being able to see the device, It's difficult to make a judgement. At a guess, I would think the usb connection may only be to charge the battery in the player. So would be better in a mains adaptor as used for other devices.
One possible reason for it not seeing the MP3's is, they may need to be in the root directory (not in any folders) of the memory card. It's a pity you are not in Fethiye. If I could see it, I may find a solution.