All of a sudden I have no sound

I am using 10.6 buster on a 64 bit Lenova all in One. I was using the puter and all was fine. I stopped to eat dinner and when I went back to the machine it would not come back up. I though maybe the keyboard needed new batteries, so I changed them. It still did not wake my machine no matter what I did. So I turned it off and then back on. Only problem is the sound is not working at all.

What do I need to do to find out why the sound just quit. Your help is greatly appreciated.