Helicopter Autorotation
This shows an R44 helicopter doing a practice autorotation.
What is a autorotation? If you loose power in a helicopter a autorotation is when the machine glides to the ground without power to the blades.
I am not a helicopter pilot yet. I am a professional videographer who has shot for a lot of years from helicopters as part of my job. This was a practice autorotation in a very controlled environment over our normal airport. So yes helicopters can fly without power as long as you still have blades rotating, altitude, and a skilled pilot.
Here is the clip of one of our autorotations from onboard looking out the side door. Autorotation