There are several possible problems.
1st - I have had many HDMI cables go bad. I highly suggest using on HDMI version 1.4 cables - there are version 2.0 cables and they work too. Cables from a reputable company are a must. I have used cheap cables and they are intermittent and usually fail completely after a while. Belkin, cables 2 go and other cables are more expensive but I have never had any of them fail. Test the cable on a known good working system to see the picture and audio working for yourself.
2nd - If you computer received updates, I'd go through Device Manager and check for any devices not properly recognized and fix those errors.
3rd - Go to Control Panel, Click on Hardware and Sound, Click on Sound, find your device and ensure it is enabled.
4th - Check Bios on your computer and check it the HDMI port has been turned off.
5th - If you are running this to a TV, the TV may be at fault, check by going through the TV menus. Or - check by attaching your computer to another HDMI enabled device.
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