The plug-in isn't using the right microphone, speaker or webcam device
If the Hangouts plugin is not using the correct microphone, speaker or webcam device, please check that the device you wish to use is properly plugged into your computer and that no other open programs are using it. Once you have done so, you can change your settings.
Caroline is a Hangouts expert and author of this help page. Leave her feedback below about the page.