I have just bought a brand new iMac 27 inch retina 5k, 3.2 Ghz Intel core i5, 8gb memory and 250gb flash storage..lovely machine, however when I run garageband on it the CPU in the activity monitor goes well over 100% sometimes hitting 200 and causes the screen to freeze and I get the spinning wheel although sound isn't affected. Apple support have been on it since 11 Jan and still can't sort it, any ideas? Hardware or software prob?