My camera had the same symptoms, and the problem was the stuck shutter. If you take off the lens and see the closed shutter then it's likely a stuck shutter problem like mine. My camera is working now and I see the sensor when the lens is off. I don't have a fix to recommend because the shutter retracted by itself when I accidentally dropped the camera on the floor while trying to take it apart. Perhaps someone has posted a proper way to fix a stuck shutter. Good luck. :)