Without music again

Sigh. So I spent an hour or so fiddling with my mp3 player getting a new 2Gb playlist transferred. Unmounted everything properly so that there was no file corruption risk. Unplug the USB and turn the power on. No music files. I have no idea what has gone wrong but whatever it is it has left me without music this evening and potentially Monday morning too depending on what mp3 files I can find laying around on hard disks at home.