I am not sure why music tracks will not drag and drop onto the timeline for you. The only thing I can think of is sometimes it is possible to have PhotoVidShow running in a higher administrator privilege than your explorer window. In these cases Windows will disallow drag and drop.
However, there are plenty of other ways to add music to the storyboard:-
-Select the ‘Add background music to the slideshow’ button. Bottom left, navigate to your music, select the music you wish to add, then select ‘Open’
-Also from the ‘Edit music track list’ window there is an ‘add’ button. This window can be brought up by selecting the arrow next to the ‘Add background music to the slideshow’ button and select ‘Add or edit slideshow music track list’. You can also simply double click a music bar in the storyboard to bring up the track list window once music has already been added. Hope something here of help