Tuner and Chord Trainer not working in Garageband

I am experiencing problems with Garageband (version 2011) which I haven't used for several months. The last time I used it, it was working fine but now the chord trainer and tuner doesn't appear to be working as it's not picking up any sound. I haven't made any changes so don't know how its happened. Could this mean a fault with the software or have I missed something obvious?

Thank you.