Installing a theme with a themepack extension in Windows 7
You can find Windows 7 themes on Microsoft’s dedicated site.
After downloading the chosen themes, you normally only need to double click on the freshly downloaded *.themepack files to install them.
However, due to system corruptions, you may not be unable to do so, with no correct program being associated with the .themepack extension on your PC.
If you face this problem, go to Windows Seven Forum “Windows 7 – Default File Type Associations – Restore” tutorial, search for “themepack”, download the tiny “reg” file, run it, and bingo, you should now be able to install files with a .themepack extension without problem :)