Well, I have made a breakthrough! (of sorts). My vid card only has DVI out but my monitor has DVI and VGA. Using an adaptor I used a VGA connector instead, and got video using only the "failsafe" command. However, I have no mouse control (plugged into PS2 port) and it's horrifically unstable.

Anyway, I'm off for a drink. Hope this info may be useful to someone else: black screen but sound - use VGA.