Hi, qzxcvbn!
I think i have a similar problem with my Bvision. You say that your BVision is fine because you can see the workbench screen. Hmm, are you using an AGA or a CGX screenmode?
I can use an AGA screenmode like before installing the card, but when i try a CGX one, i only get an empty grey screen. (or a black one, like in your case, if i'm using a borderblank utility)