Q: Why has Enhanced Dictation stopped working?

A few days ago when I turned my computer back on, I found that Enhanced Dictation no longer worked for any of the applications into which I usually dictate.  This persists and I can no longer dictate in my own user account (Enhanced Dictation does still work for other user accounts).  When I have Enhanced Dictation active now, the microphone icon shows that it hears what I say but no spoken command get obeyed and no text displays in my active application.  If I turn Enhanced off, Dictation does work but I cannot see the point of using Dictation without access to spoken commands and with the delay inherent in sending dictated text to Apple and waiting for it to return as text.  What could have happened?