The thing i have done before this problem was I have done few setups using Theme Customizer which done a reboot after the changes applied. This I have done for 2-3 times where the phone rebooted after each setup..The problem occurred when there was a fourth time reboot..Hope I should have not done such frequent theme settings change and reboot after that.
Before this, I have a problem with the camera which shows "Operation failed" whenever i try to use it. So I uninstalled the relevant apps for the camera hoping that may work after that. But the problem was still existing even after I had cleared some space in the phone memory which was suggested by few forums.