You run out of arcane power (mana) as a Mage in D3?
You must be playing the game wrong. Really wrong. Lol.
If you're getting one hit check the AH, buy gear with more vitality.
And yes, it took you a while it seems but you finally realized D3 ain't D2. You were expecting the wrong thing. And this is coming from portably the most hardcore D2 player you have spoken with.