No sound auditioning in Media, and I crash in trac view

I'm going through the tutorial X2 Explained. I can't audition loops in Media, and if I drag them into a trac, Sonar crashes. here is the history and detailed evolution of my problem: I did the following SUCCESSFULLY a couple times but then had these results: I go to Project File, choose Blank, go to Browser>Media>Loops>Loopmaster>World of Jazz (actually ANY loop from here on results in the same thing)>Jazz Session> and I'm choosing the top or the list that opens (although again any choice will result the same), and with Auto Preview selected in Media, and having set up my Stereo Preview Bus in Console view, I get no sound. At first I COULD get the sounds to audition. I even drug a drum set into a trac and played it, and added a bass from Media, and played them together. THE PROBLEM BEGINS: After this success, I closed Sonar and started over (for practice), but I could no longer audition sounds in Media unless I drug them into a trac. Now as I start over (practicing) and press Play for any of these loops I've drug into my tracs (still won't play in Media), Sonar crashes - every time - at that point. There seems to be "gradual degradation" going on. What might I be doing unconsciously? Any ideas? Thanks.