What is wrong with a locked-up Stihl 011 ATV?

My Stihl 011 ATV was locked-up, when I bought it. I loosened the nut on the flywheel and immediately, I could turn over the piston by hand. I cleaned the spark plug and dried it thoroughly. The oil/gas ratio might have been the problem, but I have not put in a correct fuel mixture yet; however, this does not seem to be the problem - the chainsaw did fire once with the previous fuel mixture in it. In spite of all of this, after I try to start the engine by pulling the rope four or five times, everything locks up again. Also, has anybody else had trouble with the high-impact plastic handle breaking back toward the posterior end on this model?