schwegs,

First I would remove the glow plug and see if it will turn over. It could be hydra-locked. If that is not the case drop the motor and see if you can turn it over with your hand. If mine was not hydr-locked usually the the nut that holds the fan on had backed off and allowed the fan to unscrew and lock up the system. If you get it out and can not turn the motor over by hand.... You may want to contact the manufacturer.

Hope this helps!