Simple answer: your input (the right-pointing arrow) is set to None! Click on it and change it to whatever input you want to use that's shown as available. If there are no inputs available you need to look at your hardware settings.
Simple answer: your input (the right-pointing arrow) is set to None! Click on it and change it to whatever input you want to use that's shown as available. If there are no inputs available you need to look at your hardware settings.