In Diablo 3 for the PC, you can’t just jump into the hardest difficulties right away, because the game is level and equipment based. You might think you were a D2 badass, but trust me.. the hardest difficulty in D3 is not done lightly.
In order to unlock the different difficulties, you just need to beat them, and attain a certain level.
Nightmare Difficulty – Beat all four Acts on Normal, and be level 30
Hell Difficulty –Â Beat all four Acts on Nightmare, and be level 50
Inferno Difficulty –Â Beat all four Acts on Hell, and be level 60