Camera powers on then powers off as if lens is stuck

I have a Canon Powershot S3 iS. When I power it ON on camera mode, it doesn't do anything but has a little buzzing then powers off on it's own. BUT when I switch it to the picture view only. I can see all my pictures and edit. but as soon as I switch to camera mode. it buzzes and powers off after a few seconds. What can it be?