have you tried using just the integrated speakers on the monitor?, maybe its the audio jack itself. Also, you might've tried this already, but in the bottom right of your taskbar, the volume thing, if you right-click on it and hit 'playback devices' and then set your monitor as the default output. It seems from the picture you've already done this, but maybe just double check that it is the right device by plugging the hdmi cable in and then out and then in again, and then seeing which device pops up in the device manager