Mbox & Garageband help please

Hey guys, I am very new at all this so I will try my best to explain what is happening without getting everyone confused. I am currently using an Mbox and garage band on an intel Macbook pro to do very simple recordings (think one basic instrumental track and a vocal track). I also have Digi CoreAudio Manager installed. For some reason I do not get any kind of playback in my headphones. As you know I can't really do any vocals without hearing the track in the headphones or having the music being played without the microphone picking up the music coming through the speakers. I have tried all the settings in garage band and turning all the knobs on the Mbox but, nothing seems to work. I googled the hell out of this question and couldn't find any kind of answer or even something as simple as a walk through set up. I am sure its something simple but, I don't know what. It did work for me before but I haven't touched garage band or the Mbox since March. What could I be doing wrong? Hopefully I have explained this clearly. I am so glad that forums like this are around!