When you use the Windows Disk Management snap-in tool to mark your primary partition as active, the computer may not start up if the partition marked as active does not contain the Windows boot files (or boot files for another operating system).
NOTE: When this happens, you may receive the error message when you try to start the computer:
NTLDR is missing
This problem occurs because on Intel-based computers, the system partition must be a primary partition that has been marked as active for startup purposes. This partition must be located on the disk that the computer gains access to when starting up the computer. There can be only one active system partition at a time. If you want to use another operating system, you must first mark its system partition as active before restarting the computer.
To resolve this problem, perform one of the following:
It may be possible to change the active partition by booting to a floppy disk and using disk utilities to manually change the active partition.-or-
If enough free disk space is available, you can install Windows to a parallel directory. After the parallel installation is complete, you can use the Disk Management snap-in to change the active partition.
The names commonly used for partitions containing the startup and operatingsystem files are system and boot partitions, respectively.-or-
If the partition that has been incorrectly marked as active is a FAT, FAT32, or NTFS partition, you may be able to correct the problem by using the Windows Recovery Console.
For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
229716 Description of the Windows 2000 Recovery Console
NOTE: Windows always considers the active partition to be drive C, so the drive letters on the hard disk partitions may have changed from their original orientation. Using the Recovery Console, you need to copy the following files from the root directory of the original system partition to the root directory of the current active partition (which is now drive C):
NTLDR NTDETECT.COM BOOT.INI
If the partition was not formatted using Windows, you may also need to use the Recovery Console's FIXBOOT command to make the active partition bootable.
After you are able to boot into Windows, it is recommended that you use the Windows Disk Management snap-in tool to reset the original system partition as the active partition, and reboot the computer. This will restore the correct system partition as the C: drive.