If Windows Vista is installed on the active partition and you dual boot between Windows Vista and Windows XP, deleting or reformatting the Windows Vista partition prevents Windows XP from starting.
This behavior occurs because reformatting or deleting the active partition removed the Windows XP startup information.
To restore the Windows XP startup information:
1. Insert the Windows XP CD-ROM in your CD-ROM or DVD-ROM drive.
2. Restart your computer.
3. When you see Press any key to boot from CD press any key.
4. The Welcome to Setup page displays:
This portion of the Setup program prepares Microsoft Windows XP to run on your computer: To setup Windows XP now, press ENTER. To repair a Windows XP installation using Recovery Console, press R. To quit Setup without installing Windows XP, press F3.5. Press Enter to begin the repair process.
5. Press F8 to accept the license agreement on the Windows XP Licensing Agreement page.
6. Select the installation of Windows XP that you want to repair and press R.
7. After completing the repair, you may have to reactivate Windows XP.