Your Audio Control panel should be set to HDMI AMD. If you changed it from that, set it back. Next make sure that the volume on the monitor is set high enough so you can hear it (on screen display of your monitor).
If that doesn't resolve the issue, change the audio control panel back to your analog output and plug in a 3.5mm stereo cable (speakers) from your PCs onboard sound to the line in on your monitor. See if you can get sound that way.
-Wolf sends