GarageBand '09: No sound from guitar when playing lessons
Sometimes you may not be able to hear your guitar when you play along with a lesson in GarageBand '09.
If you are unable to hear your electric guitar when you play along with guitar lessons, check your setup to verify you are connected properly.
From the lesson window, click Setup in the upper-right corner.
From the "My Input Device" menu, choose Guitar if your electric guitar is plugged into the built-in line input on your computer; if it's plugged into an external audio interface, choose External Guitar.
Note: To play along with lessons, the guitar must be plugged into the first input of your audio interface.
After you have checked your guitar input, verify "Monitor On" is selected from the "My Input Device" menu.