Harry potter 5 question?

In harry potter and the order of the phoenix movie when bellatrix lestrange killed sirius black, Harry got really mad and chased her and then he pointed his wand towards her and said crucio, why didnt she roll in pain when he said that, why did she just fall over, isnt crucio the torture curse?. One more question, In harry potter and the half blood prince why does every one who has read the book say that they missed a entire battle which battle? Thanks for answers.