Use the Sound applet in control panel to check what audio devices are installed. If you have a choice make sure the right one is selected.
With 11 pages on this thread and it is already answered few are going to see your question and have you read it through and looked at the possible solutions? If you have then it might be better to start your own question.
Detail what you have tried and what your hardware is, with laptops because everything is on the motherboard getting audio onto the HDMI is normally inbuilt but with desktops it could be different. Even with a desktop if you are using an integrated HDMI/sound
card then that is the same as a laptop but if you have a discrete graphics/sound interface then that requires different settings.