Originally Posted by MarkN

I think the flywheel bolts are staggered so it will only bolt up in one place. Even if it were in the wrong place - it would still spark and fire the injectors but the timing would be wrong and the car wouldn't run.

Did you accidentally clout the sensor when you took the flywheel off? Might be worth trying a different one. It's less likely to be a speed sensor as this is primarily used by the ECU to sense overrun, and wouldn't stop the car from starting.