1. Insert the Windows Vista installation disc.
2. Click the Start button Start button, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator. Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
3. Type [DVD drive letter]:\boot\bootsect.exe /nt52 ALL /force and then press ENTER.
For example, if the DVD drive letter is F, type f:\boot\ bootsect.exe /nt52 ALL /force.
4. Eject the Windows Vista installation disc.
5. Restart your computer.
Your computer will start in the previous version of Windows that you have installed.
6. Delete Windows Vista files and folders, such as the Program Files, Users, and Windows folders, manually.
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