Gizmo (manipulator) is missing for some reason I have a problem with gizmo 
(I am not sure what it called but it is the three arrows of axes when you scale, rotate, move).

it disappears sometimes and I can't get it back unless I open a new project. Can please some one help me with that?

I am using Blender 2.8.
When I press Ctrl+Space the show gizmo box is checked.
I was clicking Space bar by accident and i didn't realize it is going frame by frame until i saw the info datum that shows top left ... Fixed by clicking the space key