If you managed to go into Disk Management in Windows XP and somehow click “Mark Partition as Active” accidentally, this could render your computer unbootable. If you are so lucky that you haven’t rebooted yet, here is one possible solution to the problem: mark the partition as inactive using the DISKPART tool:
- Open up a command prompt and type DISKPART.
- Type LIST DISK
- Type SELECT DISK n (where n is the number of the old Win98 drive)
- Type LIST PARTITION
- Type SELECT PARTITION n (where n is the number of the active partition you wish to make inactive)
- Type INACTIVE
- Type EXIT to exit DISKPART
- Type EXIT again to exit the command prompt
If you have problems booting your computer or the above approach didn’t work for you, you could also try what Microsoft suggests on their help page entitled The computer does not start after you change the active partition by using the Disk Management tool – external link, opens in new window. For your convenience, the content of that page is reproduced below:
After you use the Windows Disk Management snap-in tool to mark your primary partition as active, the computer may not start, and you may receive the following error message:
NTLDR is missing.
Press Ctrl+Alt+Del to restart.
This behavior occurs if the partition marked as active does not contain the Windows boot files or the boot files for another operating system. 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 at startup. 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.
IMPORTANT! Before performing the steps listed below, make sure that you have a good backup of your critical data files.
To resolve this behavior, use one of the following procedures:
• Try changing the active partition by booting to a floppy disk and then using disk utilities to manually change the active partition:
1. Boot to a command prompt by using a Microsoft Windows 95, Microsoft Windows 98, or Microsoft Windows Millennium Edition (Me) boot floppy disk.
2. At the command prompt, type fdisk, and then press ENTER.
3. When you are prompted to enable large disk support, click Yes.
4. Click Set active partition, press the number of the partition that you want to make active, and then press ENTER.
5. Press ESC.
6. Remove the boot floppy disk, and then restart the computer.
• Boot the computer by using a Windows XP boot disk. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
305595 How to create a boot disk for an NTFS or FAT partition in Windows XP
• If the partition that has been incorrectly marked as active is formatted in the FAT file system, the FAT32 file system, or the NTFS file system, you may be able to use the Windows Recovery Console to correct the behavior. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
NOTE: The system partition refers to the disk volume that contains the files that are needed to start Windows (for example, Ntldr,Boot.ini, and Ntdetect.com). On Intel x86-based computers, the system partition must be a primary partition that is marked active. On Intel x86 computers, this is always drive 0, the drive that the system BIOS searches when the operating system starts.
Using the Recovery Console, copy the Ntldr file from the Windows XP CD-ROM to the root directory of the current active partition. Follow these steps:
1. Start your computer by using the Windows XP Setup floppy disks or by using the Windows XP CD-ROM.
2. At the “Welcome to Setup” screen, press F10, or press R to repair.
3. Press C to start the Recovery Console.
4. Copy the Ntldr file from the Windows XP CD-ROM to the root of your system partition by using the following commands, pressing ENTER after each command: a. Type cd .. to go to the root of drive C.
Note that there is a space between the d and the two periods (..).
b. Type the letter of the CD-ROM drive.
c. Type cd i386.
d. Type Copy ntldr c:.
e. Type Copy ntdetect.com c:.
f. Type Bootcfg /add.
g. Type Exit.
If the partition was not formatted by using Windows, you might also need to run the Recovery Console fixboot command to make the active partition bootable.
After you can 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 then restart the computer.