How do I activate the editing box at bottom of "Tools" section? When I add a new item (sphere, cube etc) the lower left hand editing box is no longer activated....it is clouded over and unresponsive. For example: I add a UV Sphere but can no longer change the segments, rings, size etc. It was working in the past which makes me wonder if I have inadvertently turned it off....I have closed and reopened Blender but cannot rectify this issue.
in 3D view, use T to make the toolshlef appear/disapear.

You can also use F6 to get the specific toolbox for new objects