You unlock Master once you beat the game and you unlock Torment once you hit 60 with a character so you should have all the difficulties unlocked. If you're asking why you can't do higher than Hard, then the answer is pretty much always, "You need better gear." After a quick glance at your character, I feel like an easy way to raise your dps is to get more crit chance. You're missing it on your amulet, both rings, and your shield.