When I run MAX2, I get black screen. Sound is played and the game works, but nothing is displayed, dunno why...

I had same problem. I have no idea what caused the error or how to fix it. But for some odd reason I'm not plagued by the black screen. Try running the M.A.X. Graphic Mode Setup(Start => GOG.com => M.A.X. 1 and 2 => M.A.X) and then run M.A.X. 2.