Windows App Permissions! I suddenly experienced this problem after a Windows update. The microphone no longer worked in Discord and other applications. After a lot of research, I found the culprit in the Windows microphone app permissions. "Allow apps to access your microphone" is the name of the thing. Just type this in via Start--> Search and you will find this setting, there you can make finer settings at the bottom. Hope this helps you and all those who have been desperately searching for it! :)