Cant hear real instruments on playback in Garage band

Can anyone tell me why I can't hear the real instruments in my song in garage band version 5.1 on macbook. I could hear everything while recording the tracks and the last time I listened to the song but now all I can hear are the software instruments. I can see the WAV data and the VU meters are moving on every track. I opened up a different song and I could here the real instrument on it. All settings etc are the same , nothing is solo'd, ? ! Any ideas please ? !