Pictures are over exposed except when in low light

The cable to the shutter has broken, causing the shutter to remain open - overexposing everything but low-light pictures. You can find a replacement cable on ebay...But it is far too difficult to install (the lens assembly must be disassembled, and the cable needs to be soldered). If you you handy, you can replace the whole lens, which includes the cable. You can find new replacement lenses in ebay for about $35.

Your camera might be set to a high ISO number. Change it to "auto ISO". It might also be in night scene mode. Why not try a camera reset? Go into the setup menu and scroll to "reset" and follow the on-screen instructions.

If it is the shutter flex cable has broken , you can buy it at following address at great price .

http://www.think-tec.com/sdp/802780/4/pd-4240360/5324944-1805888/Digital_casio_Casio_camera_flex_cable_for_replacem.html