Ixus 50 / SD400 hangs on startup

My Ixus has orked fine for a long time and but now it hangs during startup. What happens is that the Startup picture is displayed, the lens comes out and then it just hangs. No buttons work, and no error message on the display (No E18 or anything like that). After a few seconds the camera turns off. If I turn it back on, the lens retracts just fine, the startup image comes on the lens comes out, and it hangs again. Shuts off after a few seconds. This is the same for both phto and video mode. Starting up in playback and then switching to other mode gives the same result. Playback seems to work fine, althoug I don't have any pics on the memory card. Menus and changing settings when started in playback mode work just fine.