I just got Civ 5 for my macbook (late 2008 version) anyway after i finished downloading it from steam( you don't load it from the disc apparently) and it started to load and it plays the intro movie then about half way through it freezes and "unexpectedly Quits" i try again and finishes but goes black and quits THEN i do it again and i see a glimpse of the menu for about 3 seconds. Then it goes black and quits. Why is it doing this?