'Just copy this procedure. It shows all shapes in a presentation
'that have been made invisible.
Sub ShowItAll()
    Dim oSld As Slide
    Dim oShp As Shape
    
    For Each oSld In ActivePresentation.Slides
        For Each oShp In oSld.Shapes
            oShp.Visible = True
        Next oShp
    Next oSld
End Sub

'This procedure is just used for testing. Assign it to a shape and click
'on the shape in Slide Show view for it to go away. It should come back when
'running the above procedure.
Sub HideMe(oShp As Shape)
    oShp.Visible = False
End Sub