To unhide all the hidden file extensions on your system, follow these steps:
Click the Windows Start button and open the Control Panel.
From the Control Panel, select Appearance and Themes from the Category view.
Double-click the Folder Options icon.
When the Folder Options dialog box appears, select the View tab.
Scroll down the Advanced Settings until you come to the Hide Extensions for Known File Types item.
Uncheck the Hide Extensions for Known File Types option.
Click OK to register your changes.