Speakers quit working

So the speakers are on the monitor?
Have you tried it on another PC/laptop?
Uninstall/reinstall drivers?

If none of the above work then your onboard audio may have stopped working. its not uncommon for the onboard audio on motherboards to give out. Short of an RMA, you can get a audio USB adapter from your local PC shop

First of all, the onboard audio has nothing to do with the hdmi sound. The HD6570 has it's own audio chip. You say you can not get the speaker setup to work? Is the standard playback device still set to HDMI? Do you see the bars moving next to it, when playing a soundfile?

The playback device is set to ATI HDMI Output. The little green bars go up and down indicating that the software is producing sound. I tried plugging in a headset to the front of the tower and no joy. Also, the ATI HDMI is set as the default. I also have a Creative SB X-Fi sound card that I use for something else and shouldn't be a factor, I believe. I'm stumped unless there's a hardware issue with the video card.