If you have gone in for the option to upgrade your Windows OS, and if you find that the upgrade attempt has failed and you get an error message:
This version of Windows could not be installed, Your previous version of Windows has been restored, and you can continue to use it
The PC on subsequent reboot/s keeps showing you the same message.
In such cases, you may want to try the following:
1. Select Windows the existing version name instead of the default Windows setup when you see the boot entry menu.
2. Insert the Windows Media of the existing version into the drive and exit the Windows Setup when its launched
3. Click Start > All Programs > Accessories > Right click the Command Prompt icon > Click Run as Administrator.
4. Type the following command at a command prompt and hit ENTER
Drive:\boot\Bootsect.exe /NT60 All
In this command, Drive is the drive where the Windows (existing) installation media is located.
5. Restart your PC.