You must have disabled the thumbnails view for the files and folders. To enable it back, do as following:
- Go to START, next ALL PROGRAMS, then ACCESSORIES.
- Now WINDOWS EXPLORER has to be run.
- There, select the ORGANIZE button which is located on the menu/shortcut bar.
- In the DROP-DOWN menu, select the FOLDER AND SEARCH OPTIONS.
- Now, in the FOLDER OPTIONS dialog, click on the VIEW tab.
- Here, the checkbox needs to be checked in ALWAYS SHOW ICONS, NEVER THUMBNAILS OPTION.
- Finally click on the OK button.
