I help run the soundboard and computer at church, and we just replaced our computer. At first, everything was fine- Audacity was recording our messages with no problems. Then we had the need to add another monitor (to display the song lyrics through projectors). Well, to do that we had to connect the 2nd monitor with an HDMI cable, using an HDMI converter. Well, once we connected the 2nd monitor with the HDMI cable, Audacity would no longer recognize audio coming through the microphone (trying to record the messages). It will still record anything coming from the computer, but does not recognize any sound coming from the microphone, which is wireless, connected to the soundboard, which is connected to the computer.
My guess is that Audacity is trying to record the HDMI audio instead of the microphone. Check the settings in the device toolbar and ensure that you have the correct recording device selected.
Thank you for your response, Steve. I have tried changing that with no success. I have 2 options to choose from there- “Microsoft Sound Mapper - Input” and “Stereo Mix (2 - Realtek High Def” Choosing either one of those results in the same problem. Still a flat line.
I figured it out! It was an issue with the connections, and I got it worked out. 
We are having the same problem. Could you tell me what you did to fix the issue?