So all the sudden 16.04 removed the "lock" system menu (top right menu button); also "dimmed" from "Brightness & Lock" system settings. Computer no longer displays screen saver. When forced to turn off screen, no passowrd required to reactivate the session.
What gives? How to resolve other than reinstalling 16.04 64-bit?
TIA, John
System settings: System settings screenshot
About computer menu: Ubuntu Unity menu (top righthand corner) missing "lock" session option
Just as another user remarked, I solved my problem by running unity-tweak-tool and removed check disabling "Desktop Lock". I don't know how this got disabled in the first place!?!