Question
I used my lawn sprinkler system on Thursday.....that night, the pump came on automatically. I had to shut it off at the power source. It continues to run when plugged in but delivers no water.

Any help appreciated.

Answer
Without knowing the particulars of your system, it is hard to say what the problem could be.  The fact that it isnt pumping water when on is puzzling.  It could be the relay that tells the pump to come on is bad, and has stuck in the open position.  But if the sprinklers arent operating then I would suspect that there is another problem with the irrigation controller.  Or maybe the pump and the irrigation controller are out of sync.  Sounds like you need a local service person to evaluate it.