Have you pressed the song title on the main screen that you want to play on the floppy? You must select the song you want to play by pressing the button next to the song? do the preset songs play, i.e when you press the button next to "Amazing Grace" (button A) and then "Start" in song control, does the song play. If you have not selected a song then the Start/Stop button will NOT light up.
I doubt if the Hard drive would cause the problem you describe.
Hope this helps.