The preview seems to use the overlay technique, which is incompatible to Aero and thus should be avoided! My preview is not working either and I've reported this several times, but nobody seems to care.
I just found out that when I move the DVDFab window constantly, the preview is working, but as soon as I keep the window still, it freezes again. This is clearly a bug of DVDFab! Something with the refresh of the overlay surface is wrong, but I guess nobody cares and so the problem will not be fixed.