I would guess if you had carbon break away from the head and jam the piston from getting to TDC the first thing would be for me to turn the crank counter clockwise to see if the piston seized. If it did the for sure you had something stopping the piston. At that point removal of the head and further examination. If turning the crank backwards reveled a short free spin then grab the I would be thinking a cracked main bearing or wrist pin problem. If it just went CLUNK and free spun 200 deg then bye bye rod. There are numerous things to look for and check along the way. But spraying Smelling salts down the bore is not the most wisest thing to do in the first place. Reminds me when we raced Go karts and blew into fuel tanks to prime the Carbs so they started first pull. Talk about killing grey matter.