Apple Logic Pro /LogicExpress Discussion

For some reason, my loops don't playback. I have Logic Pro (just installed) and Logic Express and Garageband. When I audition a loop, it plays just fine in all three systems. In Logic Pro and Express, after I add a track and drag a loop, the loop track is added but there is no sound. I've checked my audio settings and now have all my monitoring equipment unhooked and the audio setting on using the internal speakers. In Garageband, the loop plays just fine. Help!