So if I’m understanding you correctly, you’re saying that the player itself can’t find any songs (Artist, Album, etc, lists show as EMPTY) and when you connect to your computer Windows Explorer doesn’t show any files either? What the the player say about used and available memory space if you go into Settings > System Settings > Info? Likewise, if when connected to the computer, if you right-click on the player’s drive and select Properties, it show you used and available memory space. What is this telling you?
Are you by any chance ‘syncing’ with Windows Media Player? And if you are, have you deleted the songs from your computer (or moved them to a different location on the computer)? If so, when you plug in your player, WMP won’t locate these files on your computer and therefore will automatically delete them from your player as well.