I used Mumble last night for Tf2 competitive and now the only sound my laptop produces is Mumble-related e.g. when someone joins a server or using the Audio Wizard. I am unable to hear the audio on videos or any in-game sounds. I've tried uninstalling it and stopping the task via the control panel.
Check the audio levels in the windows audio mixer and see if the other applications are at 0% volume there. Did you run two mumble instances at the same time? In this case they can interact badly and fail to restore audio levels correctly after lowering them.