"doom upon all the world" crashes on the first cutscene!

So, im about to finally beat the game after 100 hours, and when i start the final mission, just when Corypheus is killing those soldiers at the beggining, the audio starts bugging out, and after that the animations start bugging out too... so if i leave it there, i can see characters in the background just standing there and well, everything is messed up. By skipping a little i could advance a little to a conversation with the Inquisitor and Corypheus, but after that the game just crashed!, so i have no way to beat the game! is there anything i can do?