alright, well if it gets through the bios stuff with video then it is obviously a windows issue, which is at least a helpful start.
if you boot it with the PCI card, after the screen goes black, have you tried switching the VGA connector back to the on-board video without restarting? if the on-board does have video in that case, then windows must be ignoring the BIOS default video device... Can you entirely disable the on-board video in the BIOS? (rather than just setting the default to PCI)
also, try enabling both displays in windows if dual-display is possible... basically see if you can get any signs of life out of the PCI card when in windows. probably easier if you have 2 monitors to hook up at the same time.