Why couldn't someone just bring Dumbledore back to life?

I was thinking about it when I finished the Half Blood Prince (novel) yesterday, and why didn’t someone just bring Dumbledore back to life? Harry had used a killing spell on Malfoy and Snape brought him back to life, so why couldn’t someone bring Dumbledore back?

And also… why didn’t they take Snape to Wizard Jail? Azkaban, or something, I can’t remember.