The good think about the A4000 is that none of it's connector are standard :lol:
The video-out is a D23 instead of the usual 15-Pin, but you might have gotten an adaptor with the A4000.
Problem is, the basic screenmode of the A4000 has 15kHz, while most modern monitors won't accept anything below 30kHz.
So you either need to search a working monitor (some of these combined LCD-TV-VGA thingies might work), or you need a flickerfixer-scandoubler.
Mouse and KBD do use normal connectors, but don't even think about putting a PS2-kbd or a serial-mouse their. Unless you have another set of special adaptors...