MPMan MP-F75 MP3 Player "f400" Questions

doesnt want to play certain osngs help, my f400 mp man is freaking out. Everytime i click on a song it would say no files found, but th eformats are mp3. is there any way to reset the system? dear, ...

My MPMan F400 doesn't want to skip between directories and folders. DIR navigation is not working. turn it on and plug it in transfer your folders and mp3s and what have ya wen finished unplug it it ...