Hi,
Here's what the manual says to do when you experience this problem:
*Make sure PC audio output cable is connected to screen’s LINE IN port (or AUDIO IN port).
*Make sure the sound volume adjustment can be clearly identified.
*Make sure the System > Silence option in the monitor menu is on.
*While transferring via HDMI port but no sound is outputted, it is recommended to select AUDIO INPUT as a PC option, and make sure PC audio output cable is connected to monitor’s LINE IN port(or AUDIO IN port). [For HDMI Input only]
I'd start with those suggestions first.
Here's a link to all the manuals and drivers for you product.
Product HomepageKeep in mind the monitor itself might not be the problem a quick and easy way to find out if sound is coming out from the computer is to try a pair of speakers or some headphones. Checking that out will help us narrow down the source of the problem.
Let me know what happens with the above.
--RescueTechLA