Hi ciVic,
See
http://www.wonkity.com/~wblock/a4000hard/connvga.htmlQuote
"Connecting VGA Monitors
VGA monitors can be connected to the A4000; however, since the special circuitry in the Amiga video output can mistakenly identify a monitor as a genlock and thus cause problems, a special cable or adapter is the best way to hook them up.
All this cable really does is buffer the horizontal and vertical sync signals by double-inverting them through a TTL gate. Commodore's DB23-to-HDD15 adapter (supplied with most A4000s) used a 74HCT08 for this, but you can use a 74LS04 or other low-power TTL-level inverters (or other gates wired as inverters or buffers, of course)."
I hope this helps.
Regards, Michael
aka rockape