I thought that I was playing D3 with dark mind on (the start screen was the dark version), but maybe I accidentally turned it off. I did have some issues starting D3 that I eventually figured out.A solution for you would be to replay D3 but making sure that dark mind is on from the very beginning (judging by what you were saying, it seems like you played through D3 with dark mind off and then turned it on during D4)
I suppose there's no reason to not play the entire game again at some point to try looking for some other things I think I've missed.
Thanks for the advice.