first,
2. Now go to View tab and make sure "Always show icons, never thumbnails" option is not enabled i.e. its disabled.
If the option is enabled, uncheck the checkbox and click on Apply button.
2nd,
1. Type sysdm.cpl in RUN or Start Menu search box and press Enter. It'll open System Properties.
2. Go to "Advanced" tab and click on "Settings" button in "Performance" section.
3. Now make sure "Show thumbnails instead of icons" option is enabled.
If its not enabled, enable the option and click on Apply button.