Stuck at UV Mapping: mesh doesn't show in UV Window I'm migrating from 3DS Max to blender and its totaly confusing.

Right now I'm stuck because when I do 'Mesh->UV Unwrap->Unwrap' nothing shows in the UV/Image editor window. 

I did a render of some object and since then I don't see the mesh in uv coords.

I noticed  there were some kind of masks/layers and it's totaly non-intuitive.

Here is a screenshot: so, how to see the UV mesh?
see those mask icons on the bottom right corner of your UV/image window?

 

Select the one on the left and change it to view