I've been trying to figure out the sound effect drop out for over a year now.
Opening and closing G band has never worked, nor has opening and closing Logic, or Live...although Mad Jew is correct that the core audio has something to do with the issue, because opening Logic ect. usually Starts the problem...but never fixes it for me.
If all I need to do is unmute in audio/midi set up, then I'll feel very dumb. I'm away from my Mac, but I'll try it out later...