I know this is an over disscussed topic (as it gives thousands of searches in Google) but I am having a problem of no sound with my realtek HD sound, The red sound icon is missing from the system tray and all other forums and topics i have previously found, did alas not help at all, I have tried to re-install the drivers, updated the drivers/codecs, new video card (that was HP's level of help).
I have made sure the hdmi is enabled in Bios,what am I missing???? anyone with another suggestion that will work, would be greatly appreiciated!

Hi, Nvidia GeForce 8500 GT, Intel Core 2 Duo E8400 3.0 GHz, Realtek HD audio,

I can ony get audio via HDMI, when i boot the PC with HDMI connected and no analogue (eg.VGA) connected.

I found that this is due to HDCP and content protection, can only use digital connections only!

Is the 8500 onboard GFX?

If NOT, you will also need to connect the HD-SPDIF out from the motherboard to the GFX card, which will combine digital audio (Up to 5.1) with the HDMI port.

This may help you.

I can only get video with my HDMI connected, with or without the vga connected. I tried only using the HDMI as a monitor cable and as a sound cable, it is not due to HDCP as the LCD tv I am using can decode the video but for some reason the audio was not coming through, I will check to see if I need to connect something to get the sound going, post back when I find out. Fingers Crossed!!!!!!!

TA DAAAAAAAAAAAA. it worked, I now am a proud owner of a working HDMI enabled pc, it was a lead left disconnected inside the pc. Owe you a drink one day.!!!!!!!!!!!!! Cheers

Sorry to dig up an old(ish) thread, but I seem to be having the same problem.

The weird thing is that under the audio controls, the HDMI audio setting is showing that there should be audio playing (green audio level bars dancing up), but nothing is coming out of my speakers.

Current connection is: HDMI to LCD TV; LCD TV Optical Out to Speakers
Mobo is Asus P5Q-E with a Radeon 4850 (Sapphire, which is HDCP compliant).

If you have a look in your tower, on the sound/video card there should be a white plug, if your video card is not built in to the mother board, they need to be connected by that plug, check for a loose lead and plug it in, worked for me, any luck thats all it is.