Often on Teooh desktop, there will be slight feedback picked up by the desktop microphone. In order to ensure that there is no background noise, we have enabled a "push to talk" feature on desktops that requires that you press the blue microphone button when you'd like to talk. This is the simple answer -- if you're not being heard when you use desktop, try pressing down on the microphone icon and see if that helps.
If the problem persists, it may be because you don't have headphones and the feedback is too much for you to be heard. Try exiting the app, plugging in headphones, and trying again!