HDMI sound no longer working

I have an HP dv6-3120us, p/n: XG871UA#aba, with windows 7, 64 bit.

My HDMI audio/video had been working fine until about a week ago.  The video still works great, but I can no longer get HDMI audio, only the audio from the laptop speakers.

The ATI HDMI output, ATI High Definition Audio Device, is showing as "not plugged in".   The "set as default" for this is grayed out.

I tried uninstalling and re-installing the IDT Audio driver, but this didn't help.

The problem seemed to start after the last windows update.

Thanks

jim