Audio mute light has stopped working on HP Envy laptop...

This would appear to be quite common, in fact there are several YouTube videos and forum posts elsewhere dedicated to this problem. The light was working until the other day, and suddenly stopped - I'm not sure if it is a consequence of a recent Windows update or not, as I really didn't notice straight away. I had the same problem with my older laptop, an HP Pavilion, but managed to solve it, I think by resetting the BIOS defaults. However, I've been unable to get the light working again on my Envy laptop. Any suggestions? I think I've tried practically everything.