I have a similar problem. When I start up my laptop, I never know if the sound will happen or not. The icon at the bottom is there on the sound days but not on the silence days.
We found a way to bring it back - I have to uninstall it using start, control panel system, hardware, device manager, sound video and game controls - look for anything that shows a red X or whatever it's called, we ask it to uninstall, then restart the computer.
Or something like that.
But I don't know why the computer chooses to turn off the sound when it's been working perfectly well the night before.
If it's having a silent day, I don't bother unless there's something I want to listen to and within a day or two, the sound comes back all by itself.
Robyn