Disconnect the airline from the silencer and blow into it. Take a deep breath and blow hard and I can almost guarantee the pump will start.
If that doesn't work, and I'm betting it will, take the volute cover off and make sure the impeller can spin freely.
Going by this pic you posted in your other thread, you were running the skimmer while the water was very cloudy from adding sand. (Your skimming way to wet. Drop the water level inside the skimmer) I would not be suprised if some sand is restricting the impeller making it hard to get started.