Raw Water in Engine
DO NOT TURN THE ENGINE OVER WITH THE STARTER.
Sounds like the pistons rings may be rusted/frozen to the cylinder walls and piston grooves. Not a BIG disaster if you can act quickly - winter temperatures are on your side with respect to internal corrosion and rusting.
1.Suggest you consider to flood the crankcase, upper cylinders/combustion chambers and intake manifold with Marvel Mystery Oil. Remove the injectors and squirt in enough Marvel Oil to completely cover the piston tops. First completely drain the engine of all remaining water and old oil, then add the Marvel oil to the proper ''dipstick'' level. With the injectors removed, hand crank (ONLY) the engine to get the rings free. You may have to rock the crankshaft back and forth quite a few times to get the rings loose. Dont force it... and if still stuck... add more Marvel and wait a few days more, etc. Keep adding Marvel and attempting to hand crank the engine. Get a heater into the engine compartment and let the engine soak in the heat - to melt any ice inside the engine, etc.
With persistance, It should finally break free. Once free, hand crank the engine many times to help free the piston rings, etc. THEN you can spin a few times with the starter.
2. Once free and with the injectors out and the fuel supply shut off, take a suction dip tube and remove all excess Marvel oil from the combustion chamber (so the engine doesn''t "run away" -to infinite rpm when you finally start - have a rag handy to jam into the intake manifold opening if it attempts to explosively run at super high rpm because of all the oil inside.) drain the Marvel Oil to the proper dipstick operating level and start the engine, let run at idle WITH NO LOAD and slowly, very slowly, increase the speed until you can get 1/2 to 3/4 full rpm - keep that rag handy !!!!!!!! to stop an over rev-ing engine. This will re-polish the cylinder walls and piston ring grooves; but, if there was rust obviously there will be some (hopefully little) corrosion damage. Run until the engine is at normal operating temp. Shut down the engine and drain/change the Marvel Oil to 3/4 regular oil and 1/4 Marvel. Run the engine normally but ''gently'' - not at full load for a while. After a while (weeks) of running and normal operation load, perform a compression check (and an air-injection check of the combustion chamber) to verify that all piston rings, etc. are free in their grooves and not broken.
Lets hope that the reason you''re seized is ice and not too much rust.
You can special order the Marvel OIL in gallon containers at most auto parts supply houses.
Patience and ***not Forcing*** the engine to turn is the KEY. If you FORCE it, you will most certainly break the piston rings. a little force is OK just not a LOT of force. If you are persistent and unhurried, you can get your engine spinning again like new.
Hope this help.