No Preview Available - Windows 7 Forums
This should be incredibly simple, but it took a while...two different HowTo answers, and many other dead ends.
Explorer > Tools > Folder Options > View
Go to Control Panel, System, Advanced System Settings. (Automatically opens to Advanced screen)
On the Advanced screen, Performance, select: Settings, + then Visual Effects.
Check ALL boxes, including “Show previews and filters in folder” and “Show thumbnails instead of icons”