Imported MIDI files won't play back.

I'm trying to work on a project that involves importing a number of MIDI files of old video game music and patching them together into an accompaniment track for a guitar medley. I'm finding that most of the MIDI files I have tried so far will show up as music but will not playback. When I click the play button, simply nothing happens except for that the button is depressed as if playback were occurring.

Does anyone have a solution for this? Is there something obvious I'm missing?