I had the same problem with my canon powershot sd 400. The shutters would not shut and the lense was halfway out. When I turn on the camera, the screen saver stays on, and after a few seconds, it turns itself off. I got alittle frastrated as our Co. x-mass party was coming up soon, and I realy need to use it. I pushed the lense down so hard and the shutters closed!!!! I then wiped them with alcohol to ease the movement. Now the camera works perfect. I suggest you clean your camera shutters with a cotton bulb and alcohol, and let it dry as alcohol evaporates real quick. Good luck.
If you've replaced the batteries with fresh ones, it probably has a broken zoom assembly. It'll have to be replaced by a repair shop.
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