i bought an m audio fast track usb interface to record on garageband with but i am having trouble. i plug my guitar into the interface and plug the interface into the usb port. garageband asks if i want to change the output/input source and i do. but when once i have everything set up and im ready to record, i get no feedback at all on garageband. therefore i cant record let alone listen to myself play guitar. what am i doing wrong?