I think she might be dead.....

[clonak]

Seen it before, Definately something hit the spark plug, Possibly the piston, or as Alan said, something dropped into the cylander.
As to why it wont turn over, probably bent the piston/conrod so its jammed up. Or the conrod has snapped. Either way, head and cylander has to come off, Get the tools out and more pics.