Paul Thurott has discovered from internal Microsoft documents another method that you can use to perform a full install. To do this follow the steps below:
- Boot your computer form the Windows Vista Upgrade DVD. When you get to the setup screen, start a new setup of Vista.
- When prompted to enter your product key, Do not enter it. Instead click on the Next button and continue with the setup. This will install Vista as a 30-day trial.
- When prompted select the edition of Vista which you had purchased. So if you purchase Home Premium, select Home Premium. This is important, so do not pick a version that you did not purchase as it will affect later steps.
- Once the setup has completed and you are back at your new Vista desktop, run the setup program from the Vista DVD again from within the new Vista 30-day trial.
- Go through the setup, but this time when it asks for your product key, enter in the product key that came with your upgrade.
- When asked whether to perform an Upgrade or a Custom (advanced) install, choose the Custom (advanced) option to perform a clean install of Vista. Yes, you are performing a second installation of Vista.
- Once setup has completed for the second time you will be able to activate Windows Vista as normal. You are now left with a fresh clean install of Vista and your original Vista install has been renamed C:\Windows.old. You can now delete the Windows.old folder as it is not necessary to be on your computer.