I have no idea why I can not play L4D2 and Counter strike on Mac Pro 2010. On Macbook pro it works perfectly but I kept getting a weird message if I start the game. It was somewhat related to texture thing but I can not sure about it. I re downloaded steam client for few times and re installed games several times but nothing solved. I asked steam that I have this problem and they told me that the graphic card is old to support those game but I played those games with HD5870 and now I have gtx 1060 6gb OC version. Anyone know why?