In order to see thumbnails of your pictures in explorer, follow these steps:

  1.  Click the "View" tab in File Explorer and you will see this menu: 

    2. Highlight the "Large icons" option and close the tab again. 

If you still do not see any thumbnails, do the following:

  1. Click the "View" tab in explorer.
  2. Click the "Options" button on the right and go to the "View" tab. 

  3. Make sure the "Always show icons, never thumbnails" option is NOT marked.