When you say blocked do you mean seized as in the engine wont turn?
How are your trying to turn the engine? With the starter?
Have you taken a large breaker bar and appropriate sized socket and put it on the crankshaft nut and tried to turn it that way?
When you say took off the gearbox
do you literally mean separated the gearbox from the engine by unbolting it or put the gear
can you see in the injector hole if there is water
or rust inside the cylinder?
What kind of engine is it?
Sorry for so many questions.