Well, when I click on export to create a media file into mp3 or WAV etc, none of the options actually do anything. Dialogue box disappears, and there is not the normal box that shows the exporting progress and process executions. Nothing happens.
Without a lot more information from you it is highly unlikely that anyone will be able to help you, sorry!
As a first step, please post here screenshots of your main MM workscreen and all the screens you see from the point where you choose File>Export. Together, these may give us a clue as to what the problem is.