Try to validate your game files if you haven't.
The black screen is a random bug that also happens to me as well, but usually quitting and reloading fixes it and I carry on with my playthrough. It's not specific to a particular scene as it happens completely randomly when the game seems to be changing into a black fade screen transition.
Thank you.
I have tried quitting and reloading for over one hour, with no result.
The only thing that has worked, was reloading to a savefile where I had *just* entered the basement. Exchanged a few words with Ethel before she disappears, and then head straight for the door; whereas, in the savefile where the bug happens, I had interacted with all the cursed people surrounding it save for the blabbering elf in the corner (destroyed the mirror, removed the decapitated head, spoken with the blinded corpse, depetrified the dwarf).
Which means that ok, I have found a way to progress with the quest, however I don't think that the developers would consider a workaround a bugfix.
My questions, therefor, stands.
