How exactly Power Attack and critical hit works together?

I tried to follow the rules and check FAQs but now I need a help:

I got a 13° liv THF (two-hand fighter) and 6° liv Aegis (BAB=19) and 5° Mithic tier, with Power Attack and Mithic Power Attack (but not obviously Greater Power Attack) and 34 Strenght+Brawn (+12 mod), here are damage stats as I supposed:

    12x1.5= 18(THW)      +3(Weapon Training)      +6(Weapon Specialization+2, Greater+2, Mithic+2)      +4(Magic Weapon mod)      +3(Improved Damage from Astral skin customization)      +1(Psionic Damage from Astral skin customization)      +1(Psionic Weapon feat) and      +24(Power Attack,Mithic) = 60 for first attack and 66 for iterative (due to Backswing) 

Now the question is: Whats happens with a critical hit on each point? – I’ve found many question and I read not enough answers about it so I fall in chaos each critical hit (no more a great pleasure but a trouble)-.

and then another question regarding Power Attack and Critical hit is:

Whats happens at 15° liv (for THF archetype) and Power Attack change to Power Attack, Greater ?