All I can suggest is perhaps have one last try, following this guide step by step
also after that possibly delete and reinstall the game.
and if that doesn't work, unfortunately you may just have to wait till the next atmosphere/firmware update and hope that fixes the problem.
edit: also...
I had problems with the game just refusing to load (didn't even make it to the black screen on this game)
I also had problems where sometimes other games would just get stuck at the black screen.
It's only today I fixed all those issues, by installing the new atmosphere that dropped recently...