The No active mixer devices available error means Windows can't find a working audio driver.
Windows audio runs through a stack.
Why this matters: starting with the driver saves you from poking at settings that were never the issue.
On laptops and PCs connected to a monitor or TV over HDMI, this error sometimes appears because Windows quietly switched the default output to the display's audio, then lost it when the cable was…
If a fresh driver, a correct default device, and a system restore all fail, consider hardware.
Read the complete breakdown, fixes and what happens next.