Did you attempt to format the player when it is connected to the computer ?
If you are not familiar with the format procedure - it shortly goes like this :
1) connect the device to the computer, the same way you do to transfer songs.
2) Make sure you backup all the songs to the computer before proceeding.
2) Go to "My Computer"
3) Right click on the device, then "Format..."
4) In the "File System" selection, make sure you select "FAT". If that's not available, select "FAT32".
5) Make sure that under "Allocation unit size" you choose "Default allocation size".
6) Make sure that Quick Format is NOT ticked.
7) Click "Start" - this may take a few moments, and your player will be cleared of any songs. For the test, try to put a new song that you haven't put before and see if the player detects it.
(If you had problems with the format - it goes like something in the attached video, just pay attention to the options I remarked about)
If that doesn't work, make sure you remove the SD card from the player (if it has any SD card at all). You-Tube video "G8CDvoodIX4" placeholder (do not delete)
Good luck !