When you install an earlier version of Windows for dual booting with Windows Vista, like Windows Server 2003, or Windows XP, or Windows 2000, Windows Vista no longer starts. If you install an additional copy of Windows XP on a computer that already dual boots Windows XP and Windows Vista, you may receive Disk read error has occurred when starting your computer.

These issues occur because the startup method or Windows NT-based operating systems and the new Windows Vista startup method is incompatible. Windows Vista uses a new Boot Configuration Database (BCD) store, which contains a boot menu and all the information about operating systems that are installed on the computer. Earlier Windows NT-based operating systems on X86 computers use the boot sequence described here.

When Windows Vista starts on a BIOS-based computer, the BIOS loads the MBR and then runs the code in the boot sector which loads Bootmgr.exe (Windows Boot Manager). Bootmgr.exe parses the BCD store to enumerate the operating systems and displays the boot menu. If you select an earlier operating system to start, Bootmgr.exe transfers control to the earlier Ntldr.exe.

When you install an earlier operating system, Setup overwrites the MBR, so the Windows Boot Manager doesn't load.

To restore Windows Boot Manager:

1. Log on the earlier operating system as an administrator.

1. Open a CMD.EXE window.

2. Type CD-ROM:\boot\bootsect.exe -NT60 All and press Enter, where CD-ROM: is the drive letter that contains the Windows Vista media.

3. Restart your computer in Windows Vista.

4. Use Start / Accessories and right-click the command-prompt shortcut, pressing Run as Administrator.

5. Type the following commands, pressing Enter after each line:

NOTE: Drive: is the drive letter where Windows Vista is installed and X: is the drive letter of the active partition.

<b>Drive:\Windows\system32\Bcdedit –create \{ntldr\} –d “Description for earlier Windows version, like Windows XP”
Drive:\Windows\system32\Bcdedit –set \{ntldr\} device partition=X:
Drive:\Windows\system32\Bcdedit –set \{ntldr\} path \ntldr
Drive:\Windows\system32\Bcdedit –displayorder \{ntldr\} –addlast</b>
6. Restart the computer.