It is possible that your Windows icon cache got corrupted.
1. In Explorer, open the folder %localappdata% (C:\Users\<Your user name>\AppData\Local). Make sure that hidden and system files are being shown and then delete the file IconCache.db.
2. Now delete %appdata%\ClassicShell\DataCache.db
3. Download this ZIP file containing multiple small tools for Windows from this site:
http://www.sordum.org/dns_jumper/downloads34.php 4. Inside this ZIP, there will be a folder called "Small_Tools". We are only concerned with the tool to refresh the icon cache.
5. Extract the file named ReIconCache.exe to any folder and run it. You will see the icons getting refreshed.
6. Restart Windows and see if the icons show correctly after restarting.