all of a sudden no sound on my Apple Airbook. I can hear other things just Duolingo. Help?
Which browser are you using? I assume you've gone to other sites using that same browser?
Flash Player used to poop out on me and I wouldn't get any sound on any site, but could get sound through iTunes, etc. Maybe Flash pooped out for just Duolingo?
I did tech support for a few years, and my main approach to weird "it was just working yesterday" things is to do the following (test after each step):
Check the obvious stuff: plugged in, turned on, caps lock off, logged in, etc. Seriously.
Clear any preferences if relevant (such as clearing the browser cache): also a good opportunity to look for any preferences that may have gotten turned on and are causing the problem, like "don't play plugins automatically"
Restart the application: forces any loops that were running to stop
Close all other applications: sometimes there are interactions or the computer is actually hung up on something else
Restart the computer: sometimes the computer runs out of memory
Look for driver/software updates: sometimes the company has fixed a problem, especially if you've updated your OS or something else recently