VarAudio not making sound - HELP!

I’m in the middle of a vocal session and all of a sudden I can’t hear the audio I’m working on in VarAudio. I’ve checked the audio level control, tried soloing, etc. I’ve never had a problem with this before, it just always works so I’m sort of thrown with having no idea what to check for. Everything else is working fine. Ugh. I’m fixing pitches and making up harmonies by my eyes and then checking on playback. Anybody have any ideas. Thanks!