Powershot A310 not able to sense the objects

Question

I am able to view pictures/video (taken already) from the memory card,But when I try to take new photos/video (after putting the camera in video/photo mode) I am seeing blank screen,i.e My camera is not able to sense the objects.Can you please help me in this regard.I have tried with different battery/memory card ,same problem.ThanksSailendra