Hi,
I don't have such a busboard my self, but if it has SCSI controller on, this could be the reason why your screen is black, as an Amiga 1200 without scsi boots a lot faster than an Amiga 1200 with scsi. How long have you waited before you turned the computer off again? Could also be a problem witht the termination of the scsi chain.
And the jumpers you have set, what are they concerning?
I'm on a wild guess here, but it's better than nothing :-)
