There are some beautiful Windows 7 themes that are hidden.

1. Open Windows explorer.
2. Type “WindowsGlobalizationMCT“ in address bar.
3. You will see 5 folders, enter any 1 of the folder.
4. Go to the theme folder and double click the theme file in it.
5. Now repeat the same for the remaining 4 folders.
6. New themes will be added. 

Note: You may need to activate “Show hidden files and folder option”.