your User Preferences file may be corrupted.
Quit GarageBand and remove the file
"your Home Folder/Library/Preferences/com.apple.garageband.plist" from your User Library.
Are you using MacOS X 10.7.x Lion or Mt. Lion 10.8.x?
Then the User Library is hidden by default. You can reveal it from the Finder's "GO" menu:
Finder > Go, then hold down the options ⌥ key, until the Library appears in the drop-down menu, select it and open the Library folder. Then go to the "Preferences" sub folder and remove
your Home Folder/Library/Preferences/com.apple.garageband.plist.
Post back, if this does not help.
What do you see in the Preferences folder? Maybe you are looking at the system Library? If GarageBand ever had been running on your Mac, it must have created a preferences list.
Have a look at the GarageBand FAQ - the fix for "oddball problems" describes the removal of preferences and fixing of permissions in more detail - you should also try the permissions repair.
I have another problem. Garageband doesn't seem to be working properly since moving up to Mountain Lion. My current problem is this ;
When I go to edit the instruments to add track reverb or a compressor, there is nothing in the list where the FX used to be. Which means trashing the plist file EVERY time I want to add some sort of effect to an instrument.
Is Mountain Lion the reason?
Thanks in advance for your replies.