When attempting to upgrade from Windows Vista to Windows 7 the upgrade attempt may fail with the message “This version of Windows could not be installed, Your previous version of Windows has been restored, and you can continue to use it.”  However, the next reboot of the machine’ll launch the upgrade process again only to fail with the same message. Windows Vista’ll have been restored on the computer but the Boot Configuration Database (BCD) store has not edited to restore Windows Vista as the default booting operating system. The computer’ll continue to boot to the Windows 7 Setup and then fail until the BCD database has been restored to its previous state. To resolve (KB974078):1. Insert the Windows Vista Media into the drive and exit the Windows Vista Setup when its launched. 2. Click Start, All Programs,  Accessories, and then right-click the Command Prompt icon, and then click Run as Administrator. 3. Type the following command at a command prompt and press ENTER
Drive:\boot\Bootsect.exe /NT60 All (Note: In this command, Drive is the drive where the Windows Vista installation media is located). 4. Restart your computer