I had this same problem this year. You may have foreign material blocking your pumps internal parts from turning. Usually this is in the form of pool debris getting stuck in the impeller, but in my case a colony of ants had filled the back end of the pump and were blocking the parts on that end from turning.
A few videos on diagnosing and fixing impeller blockage:
http://www.youtube.com/watch?v=e1RWd6lae9Q
http://www.youtube.com/watch?v=WT6FaK3MX4o
http://www.youtube.com/watch?v=EGZPwCoBi-Y
In my case I had to open the back end of the pump and manually clear out A LOT of ants. Then I turned the impeller to make sure it was free, and tested it very shortly outside of the pool pump housing by plugging it in.
Good luck hope this helps.
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