Where has the microphone gone? I cannot speak into it anymore as it is not there on screen.
Since you're asking for help using the site, could you move this post to the Troubleshooting forum? Your post is likely to get a lot more attention there, because that's where the people who are willing to help with this sort of problem hang out. It will also help keep this forum easy to navigate for those who aren't part of the troubleshooting group.
Don't delete it and create a new one, just click edit, and change the topic from Duolingo to Troubleshooting. Here's a guide on how to move a post: https://www.duolingo.com/comment/16609773.
...and here's a guide on how to choose which forum to post in: [Guide] In which forum should I post my discussion?.
Which web browser are you using, if you are using Chrome, check the web url input box, in the right hand side there should be an icon with a Camera or a Micrphone, click it and grant Duolingo.