Try this: Turn camera off. Remove lens, battery, memory card. Press and hold down shutter release for 30 seconds. Insert in following order: Insert battery; try turning on camera; if no response, turn camera switch to off again go to next step; Insert Lens; try turning on camera; Should be working at this point. If you now insert the card and get the same problem again, try a different card. Also try formatting the problem card. My card wouldn't format in a PC but did successfully format with the camera. As the Canon tech explained, this process clears the camera of any corrupted data and error messages. It is often caused by cards that are not functioning optimally.