I cannot move layers up or down in Table of Contents, in any display - By Drawing Order, By Source, By Visibility, By Selection. I am using ArcMapGIS10.2. When I left-click on the layer, there is a brief appearance of a black line, as if I am about to be able to move it up or down, but then the line disappears. Also there is a brief appearance of something like a null/stop sign - but then that disappears too. I've read through previous similar questions, but cannot find a solution - Can anyone help me?