Render is all gray, tried multiple things I'm trying to render an animation I made using blender models and textures, but all I get is a grey screen on the Rendered viewport and output.

On the left there's a Rendered Camera view, and on the right my objects in the Solid Viewport


I tried doing some researching to see what I was doing wrong, but unfortunately I couldn't find anything. Here's what I've tried:


See if something is up with lighting and camera, and apparently it's not;
Disabling "Sequencer" from Render > Post Processing;
Switch from Blender Render to Cycles Render, but it didn't worked either and the output it's the same;
Copy one of the objects from the original scene and place it on a new Blender file, containing just the starting cube. When I rendered through Blender Render, I could only see the cube. However, when rendering through Cycles, it rendered both objects with their following materials.


Here's the experiment on a new Blender file, and the Rendered view shows both objects


Do you guys have any suggestions of what my problem might be?

EDIT: addded .blend file below.
You're getting a grey screen, because all your objects are set to be visible but not render. 

If you check the outliner, you'll see that your "Skybox" object, "Bola" object as well as the spheres parented to the armatures are all set to not render (the camera icon is greyed out).



For each item that should be rendering, click the camera icon beside each one in the outliner.