I'm running Civ 5 on my boot camped mac using windows xp, same way I played civ 4, but it won't run it. It wouldn't run the demo either. It seems fine during install but when I try to play it goes black for a second and then straight back to the previous screen. Steam even says I've played it "last time played is today" it will say as if it actually worked at all. Any Ideas on what I might have done wrong?