No audio in video meetings - only hear/speak if I call in too

I had to make an accommodation for a participant on Monday to join by phone (we don't usually allow phone for this particular meeting), I'm not sure what I did but now I have no computer audio during my meeting since then. I'm using a macbook air and have triple checked all my setting and done an audio test. All appear to be fine. Any ideas what I've done and how do I correct it?