In some events, you will need to change your audio's output from your HDMI cable to your desktop or laptop's speaker.
I recall when I first encountered this challenge. I needed to send audio out through my Laptop's speaker using the 3.5mm port to an audio mixer connected to many speakers at an event. I had previously tested the same connection using a VGA cable and a video cable from my Laptop to a Projector. However, I decided to go with a HDMI cable because I know it would give me the best resolution. To my dismay we had no sound coming out of the speakers.
Then I came across this solution.