Windshield Wipers appear "frozen" in the on position...what is cause?

What is your question?

This week in the freezing drizzle I turned on my windshield wipers for the first time since it was inspected last Nov/Dec. To my surprise they started up and then "froze" in the up/on position. I have since tried turning them on/off, but nothing happens. What should I have the repair shop look for?