[koala121]

You say since 2 days ago you can't keep files on it. Is that only after you disconnect it from the computer? When you connect it to the computer and copy files to it, do the files remain on the drive as long as it's connected and only disappear when you try to play them? It could be that the flash chip has failed. Also, does this player have a micro SD slot? is it possible you are copying your files to the wrong drive. If there's a micro SD card in the player, it will show up as a separate drive. If you've added any flash drives recently, you may be copying your files to that as well. Easiest way to tell, open up My Computer (if you're running windows) before you plug in your player and see which drives are added when you plug it in. If more than one drive shows up, trying moving sound files into both folders. One last tidbit. What kind of files are you moving to it? is it possible your putting files into the player that it doesn't recognize?