If you are using Windows 7 Home Basic then this is not for you.. IF you are using windows 7 Home premium or Ultimate or Professional then you can use this trick. This trick will help you to unlock the HIDDEN THEMES of your windows 7 PC.

For this you have to follow some steps –

STEP 1:
  •  Type C:\Windows\Globalization\MCT  in Run or in the start Menu
  • Press Enter.
         (Note: If  Operating System is installed in other drive, Replace that Drive-letter with C:)
STEP 2:
  • A new Window will opened and show you a list of folders
  • MCT-AU, MCT-CA, MCT-GB, MCT-US,MCT-ZA.
  • Inside this Folder, There are wallpapers for a specific country:
  • AU : Australia
  • CA :Canada
  • GB : Britain
  • US : United States
  • ZA : South Africa
STEP 3:
  • If you want to use those wallpaper and themes,
  • Go into the folder of  country
  • example:-
  • If you want to use Theme of South Africa then
  • Type C:\Windows\Globalization\MCT then go into the folder MCT-ZA
  • Double-click on the the Theme.