[Bug?] 2.75a, there are no layers.

There are no layers. See the screen shot below.

I seem to have fixed it by removing that layout and making a new one.
Strange though.

That was because you were in Local View

Say what now?

In the menu View -> View Global/Local
or press the numpad / key as a shortcut

This is enough to switch between global (that is default) and local view.

the main interest of local view is if you have a lot of object in the viewport, you can select one and switch to local view, it will only display that selected object.