Well I'm only guessing now, but I wonder if the monitor needs to be in HDMI mode to get the signal. Can you switch the input modes on the monitor to see if one of the others will pick up the signal? (Ref:- sevenforums)
Thanks for joining the graphics community.
I understand you have an issue with audio through HDMI monitor.
You may need to select proper audio output device.
a) Press the ‘Windows + D’ key on the keyboard.
b) Right Click the Volume icon and select the Playback Devices, set HDMI monitor to the default device.