Assuming this isn't a seized engine...
Have you got any other symptoms? I've had a saw jammed by a bit of stick in the sprocket (strange, but true!). It could also be something to do with the starter mechanism - I've had one of these jammed too. Try taking both sides of the crank (sprocket and chainbrake, starter mechanism) off and the plug out. The crank should now be free from anything that could stop it rotating. If it's still stuck you've probably got a serious problem.
wes
March 2009
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