There is a micro switch under the battery door on the sd chip side, near the hinge of the door. It's white in color with a black lever that catches a notch in the door to slide it toward the hinge as the door closes. The switch may be stuck or frozen or it may have gotten broke off,(no black lever protruding out of little white switch) and camara won't energize if it's not functioning perfectly. Canon's design is very poor in this area, the swtich is just a real little POS.