So I just called tech support and we got through it. It was an error with the audio driver. Didn't think to check that, but oh well. Back to normal.
I know this monitor does not have built in speakers, so that is not my issue. I had an external speaker plugged into the port on the bottom of the unit, not in the back under the cover. I had been using it this way from the start and it has always worked, yet today, I am getting now audio. I've tried moving it to the back speaker port and no audio from there either. The speaker still works because I plugged it into my phone and audio came out, so it seems that this is a problem with just the monitor. It was working just fine a few days ago, so I have no idea why it wouldn't be working now. I don't really use forums, so I'm not sure what information is helpful. As I said, I have an AW2521HFL, neither audio out port is working, but worked fine a few days ago. 
AW2521HFL, no sound