The quest where you have to go back to the Dark Brotherhood Sanctuary and the whole sanctuary is on fire and being attacked by guards of the empire. After you find Nazir I think his name was, you have to follow him up to a point where you lock yourself in a coffin because the night mother told you to "Embrace Her". When the cutscene triggers the coffin closing and you hear like World War III occurring outside, the game just stays pitch black and I press the Xbox button and the little dashboard thing won't even appear, meaning the game either froze or something.

I don't know if it's my disc or the patch, but one thing is for sure, ever since that title update the looting and opening the menu and trying to search through your inventory is a lot slower than before and very frustrating.

http://www.gamesas.com/topic/1398162-game-freeze-during-death-incarnate-dark-brotherhood-quest/ just wait out the black screen, hopefully this works for you

good luck