Most cameras have these little switches on the battery door and memory door. If the doors arnt closed fully these switches arnt depressed fully and it keeps the camera from powering up.
Sometimes and impact can alter the shape of the camera so the doors arnt square with the camera frame and this can cause a problem.
Look closly as the doors and see if you can see any little openings where a tab may push into the camera and depress a switch. Maybe pushing on the door in this area when its closed will get it to function. Canon has one on the memory door and battery door so if these 2 are opened when power is on it safly shuts the unit down so data doesnt get corrupt.
All of the sudden the camera won't power up. I've tried new and old batteries. It's like it doesn't realize there are batteries in the camera.