FYI, for anyone using the Chrome browser, r-click somewhere on this page for the context menu with an option to translate. Forum preferences allows people to choose their prefered language.
Usually the visibility of file thumbnails in the Explorer window was with people using 64-bit Windows OS with 32-bit SketchUp program installed. Those people needed to use XnView (free) or MysticThumbs to view file thumbnails. Now that SketchUp has a 64-bit installation, people using 64-bit Windows OS can see thumbnails. So as Cotty asked, we need more information about your computer and SketchUp version.