microphone not working and is on
I'm not with the tech team, but it is always a good idea to include what operating system and browser you're using when posting anything to Troubleshooting.
Now, while I'm not a tech, I hope I can offer some suggestions that might be helpful. First of all, try looking in the wiki's Trobleshooting page here: http://duolingo.wikia.com/wiki/Troubleshooting#Microphone_is_not_working
Mainly, it suggests trying a different browser and making sure there isn't too much ambient noise interrupting the sensors. (And of course making sure your volume is turned up enough and not muted. Some devices have separate volume controls for main volume, notifications, and media (my phone among them.)
If you are unable to get this problem resolved, my own suggestion is to turn off the microphone and just say everything out loud without being prompted by Duolingo. I have done this and the increased amount of speaking has boosted my retention, listening comprehension, and conversational ability.
To access settings, just hover over your username where it appears in the blue bar at the top of the screen and click "settings". Once you change the settings, don't forget to hit the green "Save" button at the top. I hope this helps! ^_^