No sound on my iMac

Thank you! It worked!

Wow, this actually worked for me too ~ thanks!

I had the same problem. I just finished watching a video on YouTube. I refreshed my cup of tea and when I came back I had no sound at all. I used the advice found here: System Preferences->Sound->Output->Internal Speakers and that did not fix the problem. I went back into System Preferences and the OUTPUT SOUND MUTE box was checked. How that happened I have no idea as I was just watching a video not moments ago. Anyway, sound is back and I am happy!