I didn't find the Enable 3D Manipulator option in User Preferences > 3D View > 3D View Global in Blender.
Thoughts?
Check User Preferences > Interface tab > Manipulation: option and dropdown.
Note that you can also disable/enable it in the footer of the 3D Viewport.
On:
Off:
Lastly, as metaphor_set points out, you can key Space to open the Search menu and search for Enable 3D Manipulator.
The button for enabling the manipulator is at the bottom of the 3D view. But the bottom panel might be hidden. Then you have to press the plus sign to show that panel:
Note: The manipulator only shows the axes for which the Transform Lock is disabled in object mode. Also, the manipulator is not shown if nothing is selected.
Ctrl
+Space
.
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