Garage doors have a manual locking system as a security measure to protect your property. If you have lost power, your door might have shut itself off and locked to keep unwanted people from gaining access to your garage and home.
In order to unlock your manually locked garage door, you just need to turn the knob or large handle located in the middle of your door. Keep turning it until you hear a click. There are two bars running from the handle that release the door to be unlocked manually, and there is also a button on it which moves the bars across to lock the door. When you turn the handle, the bars will be moved away from the edges of the garage, securing the handle in the open position.
If you have successfully unlocked your garage door but it still fails to open, get expert help from a garage door repair person.