Samsung YP-T5 MP3 Player I/O error
I had the same problem and solved it with this:
On the Samsung support page, there´s a knowledge base called "YP-T6 Or YP-MT6 Show No File And Zero Free Memory"
you need to download the latest firmare from the downloads section, then with the uptader on the PC, remove the battery from the YP-T5 or 6 and connect the USB cable to a PC while pressing and holding the play button on the YP-T. It should connect in a recovery mode which allows you to update the firmware, format the flash drive and get going again !