You can use the preview pane in Windows Explorer to see the contents of most files. If you select an e‑mail message, text file, picture, or video for example, you can see a preview of its contents without opening it in a program. The preview pane is turned off by default in Windows 7.
This will show you how to turn the Preview pane off on all Windows Explorer windows in Windows 7
To Turn “Preview Pane” Off in Windows Explorer
1. Open Windows Explorer (explorer.exe).
2. On the toolbar, click on Organize and Layout. (see screenshots below)