An overheated engine that seizes will usually restart after cooling. If this one is seized from sitting it's because the rings are stuck.
Pull out the spark plugs and try turning it by hand. Put penetrating oil like PB Blaster in the cylinders and let it work for a day or two, keep adding more and working the motor by hand. Unless the thing filled a cylinder with water it will break loose. Once free turn it over by hand until it's loose again using lots of oil. Spin it over with the starter to blow as much of the oil out before reinstalling the plugs and attempting to start it.
Take my advice, I'm not using it.