Software Instruments Not Working

Hello, my Mac arrived yesterday and I'm new to GarageBand which may mean I'm simply having a blonde-moment and have just missed something.

But otherwise, some of my software instruments don't work.

I have GarageBand and the Symphony Orchestra Jam Pack installed. What will happen is that I'll create a new track, select one of the brass or woodwind instruments, and open the 'musical typing' window where I can play the notes. The problem is that when I play them, there is no sound. I'm tapping the keys and no sound is coming out. If I select a different instrument such as the grand piano, it works fine. It's only SOME of the Symphony Orchestra instruments (and the instruments which don't work change as well. I.e. - one minute the horns arent working, and the next minute they're fine and the woodwind instruments aren't).

Other than this the system/software runs perfectly.

I've taken some shots of something I've noticed that's different between the instruments that do and don't work. See below a picture of the details box which comes up to the bottom-right of your screen when you select an instrument (that is working!);

http://i23.photobucket.com/albums/b386/Ourumov/DSC00146.jpg


But this is what comes up for the instruments that aren't working;

http://i23.photobucket.com/albums/b386/Ourumov/DSC00144.jpg

Notice that under 'Instrument Generator' it says 'None', whereas in the first picture it had details. Also the drop down menu doesn't contain anything useful, and the colours have all changed to grey.


Any help would be much appreciated, otherwise Apple might get a frustrated phone call!