You have to attack enemies within five levels of yourself (or higher than you).
If you were attacking enemies within those limits, then I can only assume you have a bug.
Edit~ thinking about it, with scaling, all enemies should be within 5 levels (except other players). So if it doesn't recharge, PVE for five minutes and rejoin.
Edited by AlexDougherty on December 23, 2014 10:58AM
People believe what they either want to be true or what they are afraid is true! Wizard's first rule
Passion rules reason Wizard's third rule
Mind what people Do, not what they say, for actions betray a lie. Wizard's fifth rule
Willfully turning aside from the truth is treason to one's self Wizard's tenth rule