the only time i had this problem is when the hdmi audio driver was not installed....make sure that is installed should be able to install only it when installing catalyst
I actually discovered the fix! I had already tried uninstalling/reinstalling the device and software (both from in and out of Safe mode), trying different HDMI ports on the monitor, different cables (because hey you never know). The device always showed as installed and there were no splats in Device Manager. It was very frustrating...
Here is how I fixed it.
I shutdown the PC. Connected a different monitor to the DVI port on the video card and booted up. I then updated the drivers for the display in Device manager and at the same time deleted the High Definition audio driver and software from Device manager. I then shutdown again. I disconnected the new monitor from the PC and booted up. After I was sure I was completely booted up I connected my LCD display back to the PC using HDMI. When I logged in I once again had sound. I have no idea why this worked but it did!