First go to the maker's site and see what they suggest.
Failing that, see if player will connect to your PC as a removable USB disk drive -- if so copy all music to your computer's hard drive.
See if the player's menus work sufficiently to get you to a setup screen which includes the option to format the player.
If not, with the player attached to the computer go to the player's drive properties (Right Click its entry in My Computer) and under Tools check the player's "disk".
If that doesn't help you may have to reformat the player using Windows and select FAT (not NTFC).