How to Fix Thumbnails Not showing in Windows 7 and Vista?

If you are seeing the images like this  instead of the miniature / thumbnail display? 

To enable thumbnail view for your images, first open the folder in question. In the Views drop-down in the Task pane, select one of the following views:

• Medium Icons
• Large Icons
• Extra Large Icons

If thumbnail previews are not generated, then open Folder Options applet via Control Panel or from Start – Search box (by running the command "control folders". In the View tab of Folder Options, uncheck the following option if it is checked

Click OK.

Thats it... It wil start to show thumbnails...

If that does not work, try clearing the thumbnail cache using the Disk Cleanup (cleanmgr.exe) tool.