i used to have the exact same problem
i turned down some graphics settings, like shader, shadows, anti aliasing, stuff like that and it helped for some reason, im only getting smaller freezes now every now and then when i open the settings or steam overlay the first time after launching the game
i now have set all graphics back to max and the freezes havent returned, no idea why (my gpu can easily handle games like bf3 and crysis2)
(when the screen turns black you dont have to alt tab out, you can just wait and when the freeze is over the screen will work again)