Problems With Logic Midi... Options

[atlus]

Hello everybody. Nice to be here!
I recently purchased a Mac Mini to get my Home Recording Studio running and I bought Logic Express 7 also. I am however having trouble with this. What I want to do is just get the keyboard up on the screen by pressing Caps Lock, and then play the keys on my computer keyboard to make a sound. However, no sound is coming out. I try recording something, and the notes appear, but nothing plays back. Also, it says No Output in the bar at the bottom. However, iTunes is working correctly, and I can record a real instrument and it plays back fine. Can somebody give me details on how to solve my problem?