Well there's your problem!

I'm no expert in the dynamics of flight, but I'm fairly certain that the props are supposed to turn.
Last week my AR Drone took a nose dive into the curb of a pavement, before pirouetting through the air to land on its feet. It's not uncommon for the drone to bounce around a little if it crashes with an odd angle, the flexible props usually bounce it harmlessly off walls, etc.
As the drone sat there I thought how lucky I was that it finished on its feet, and that I didn't need to go flipping it over again. I presses the Take Off button and watched as three of the four props turned, realising there was a problem I stabbed for the Emergency cut off button, but not before it flipped itself over and onto its back.