Acrobat 8 Pro - Pages View icon disappeared!

the column of workspace icons on the left used to start with a Pages icon, that would give me the whole left side of the workspace, displaying thumbnails of all pages, so I could rearrange pages. Somehow that icon has disappeared, and the closest I can come to the function is View, Navigation panel, Pages, which isn't nearly as convenient, or as persistent, as the original setup was.
I've explored the various preferences and setup options, can't find a way to get it back the way it was. Does anyone have any suggestions, other than a complete uninstall/reinstall ?

Fred Wagner