Sony DSC-F717 (by 2 users)

I have a Sony DSC-F717 camera which has worked well(except for the incredibly slow record time in TIFF) until now. The camera stays dark as if the shutter is stuck. I can turn the camera on, see the readings(battery, memory space etc.), view images previously recorded on the memory stick — but not see anything through the lens, either on LCD or through the Finder. Is something locked up or stuck and how do I unlock it?