Outdoor Power Equipment and Small Engines - poulan chainsaw freezes

poulan chainsaw runs normally and suddenly when shutoff to refuel locks hard. pull rope will not move at all. pulled covers and pull rope, assembly moves normally but clutch assy only moves onehalf turn. pulled plug and viewed piston travelling one half stroke before appearing to be mechanically stopped. I am at a loss to understand what could be causing this sudden mechanical lockup. Chain brake is not engaged...but saw cannot be started since pull assy is frozen. Help!!!! Anyone got ideas what could be the problem? Apparently this happened once before, and the owner just got disgusted and threw the saw into the back of the shop for about a year and it miraculously "freed" itself. Now it is frozen again.

Take the chain and bar off, the pull starter off, and see if the engine rotates by hand. If not, look at thwere the coil mounts to see if it is hitting the flywheel. If not, there is an internal rpoblem...pull the muffler and have a look in the cylinder.