I would try to turn the engine over by hand first. Us a 1/2" drive ratchet or breaker bar on the crankshaft pulley. If the engine is seized up, you have bigger problems.
Corrosion at connections is probably your next battle. Remove and clean all battery and starter cables. Use a wire brush to clean the posts and ring ends and a battery brush to clean inside the battery terminals.
You may have to remove fuses and clean connections there as well.
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