Premiere Pro won't play sound.

I started a video project in Premiere Pro and then saved it and closed it.  Now I opened it up again and I am unable to hear any sound.  I can see the audio tracks are there, but there is no sound when I play them.  I have tried a few things:

     Checked to make sure it wasn't muted. (master and individual clip volumes)

     Deleted my media cache files

     Checked my audio output which was set to default speakers or headphones as I believe it should be

The Audio Clip Mixer does not show any levels when I play it although the volume adjustment slider moves to the appropriate channels.  Also, I tried right-clicking one of the audio clips and selecting Audio Channels and running a preview and it played the audio.  So clearly the audio is still able to be played in Premiere Pro, but for some reason, it isn't playing.  I don't have much experience in Premiere Pro so assuming I have overlooked something obvious will not be taken as an insult.  I need to figure this out for my final project due tomorrow.  Please help!!!