best way to find out if its hydro locked is to remove ALL of the spark plugs and attempt to turn the engine over via the starter. Get someone else to turn it over and observe if anything comes out of the cylinders, smell it after its done turning over and if it smells like gas, then you might have a leaky injector that dumps so much fuel into a cylinder it locks it. If it smells sweet like coolant, you have a blown head gasket(s), or a cracked cylinder head leaking into the combustion chamber. If it has been sitting for a while and the engine is mechanically locked from rustin the cylinder bores, you can put a little bit of automatic transmission fluid (or pb blaster, or wd-40) in each cylinder via spark plug holes and let it sit for a whole day (24hrs) to soak in and break up the rust. Bump the ignition switch (with a fully charged battery) a few times and see if it is turning over (paint a small mark on the serpentine drive belt). Hopefully this helps you!
