It's off course obvious if you know it, but with only one big object in your scene like Piero in this case, it can be overseen: Take care that you're not in "Local View" so that switching on/off the layer visibility in the "Layer Management Addon" has an effect. Blender places the text "local" in the upper left corner of your "3D Viewport" within round brackets when you're in "Local View".
In Blender 2.8 and 2.9 a similar problem exists with the "Collections" if you unintentionally limit in "Object Mode" the visibility to a certain collection that your "Local View" object doesn't belong to. In this case you can't manipulate the vertices of your "Local View" object in "Edit Mode". I hope this helps you to avoid these two pitfalls in Blender 2.66 and 2.8/2.9.