Repair the master boot record by using the FIXMBR command from the Windows XP Recovery Console.
NOTE: For additional information about an error message that you may receive when you use the FIXMBR command, view the article in the Microsoft Knowledge Base:
266745 Error Message When You Run fixmbr Command
WARNING: If your computer is infected with a virus and you use the FIXMBR command, you may be unable to start the computer. Before you use this command, ensure that the computer is not infected with a virus.
If the primary boot partition is a FAT partition, use the FIXBOOT command from the Windows XP Recovery Console to write a new boot sector on the system partition, and then use the FIXMBR command to repair the master boot record.
You may also use Windows XP Setup to repair the installation. To do this, follow these steps:
Use the Windows XP CD-ROM to start your computer. On the Welcome to Setup screen, press ENTER to set up Windows.
Press F8 to agree to the license agreement.
Use the ARROW keys to select the Windows installation that you want to repair, and then press R.
Windows Setup repairs the installation files, Windows automatically restarts, and then Setup completes the repair of your Windows XP installation.