Can't get any display with OS 3.9

[Daedalus]

Well, if you can get the early startup screen, you should be able to boot with no startup-sequence. Once you do that, simply get rid of the screenmode.prefs file to set it back to the PAL (or NTSC) defaults. At the prompt, type

cd envarc:sys
delete screenmode.prefs

and reboot. You should then get the same screenmode that the early startup screen is, and from there use the preference programs to change your screenmode preferences as you need to.

[Daedalus]

Hmmm... Yeah, it's normally not a problem to have extra monitors in there, but might be the cause of your particular problem if you have some sort of customised setup. Normally, without screenmode.prefs, the Workbench is exactly the same screenmode as the early startup screen, so it's very strange that it's still happening. Perhaps the previous owner had a scandoubler or some funky monitor drivers for a weird monitor. Copy everything out of there, reboot and see how you get on. The 1084 should be able to do PAL and NTSC modes - my one did anyway until it died...