Thanks it-ogo. You're like a black box -- I put the sentence in, you translate, and I get to understand how you do the job. It's quite challenging.
I'll start jotting down every sentence of this sort I encounter. Eventually, I'll get some feeling. Or hang myself in despair.
Anyway.
Что мне делать? What am I to do? Question asked to some superior authority, like Gods or your dietician.
Что мне сделать, чтобы ты перестала меня мучить?
Тебе этого не понять? Can't you understand this (impossibility) ?
Тебе этого не понимать? I have no guess for this one, even assuming it is indeed something one can say.