SUMMARY
When you try to start your Microsoft Windows XP-based computer, you may receive an error message that the operating system is not found. This issue can be caused by hard disk drive failure, incorrect BIOS settings, a damaged or missing Master Boot Record (MBR), or an incorrect active partition. To resolve this issue, correct the computer's BIOS settings, use the Windows XP Recovery Console, or mark the correct partition on your hard disk drive as active.

SYMPTOMS
When you start your Microsoft Windows XP-based computer, you may receive one of the following error messages:
Operating system not found.
Missing Operating System
When you start your computer to the Recovery Console to recover functionality, you may receive an error message that is similar to the following error message:
Setup did not find any hard drives installed on your computer.

CAUSE
This issue may occur if one or more of the following conditions are true: • The basic input/output system (BIOS) does not detect the hard disk.
• The hard disk is damaged.
• Sector 0 of the physical hard disk drive has an incorrect or malformed Master Boot Record (MBR).

Note Some third-party programs or disk corruption can damage an MBR.
• An incompatible partition is marked as Active.
• A partition that contains the MBR is no longer active.

RESOLUTION
To resolve this issue, use one of the following methods, depending on your situation.

Method 1: Verify the BIOS settings
Verify the computer's BIOS settings to make sure that BIOS lists and recognizes the hard disk. See the computer documentation or contact the hardware manufacturer for information about how to verify the BIOS settings.

After you verify that the computer's BIOS detects the hard disk, restart the computer, and then test to determine whether the issue is resolved. If the issue is not resolved, or if the computer's BIOS cannot detect the hard disk, you may have issues with your hardware. Contact the hardware manufacturer to inquire about how to resolve this issue. You may have to replace the hard disk.


Method 2: Use Recovery Console
Use the fixmbr command in the Windows XP Recovery Console to repair the MBR of the startup partition.

You can enable and disable services, format drives, read and write data on a local drive (including drives that are formatted to use the NTFS file system), and perform many other administrative tasks. The Recovery Console is particularly useful if you have to repair your computer by copying a file from a disk or CD-ROM to your hard disk, or if you have to reconfigure a service that is preventing your computer from starting correctly.

If you cannot start your computer, you can run the Recovery Console from the Microsoft Windows XP startup disks or the Windows XP CD-ROM. This article describes how to perform this task.

After Windows XP is installed on your computer, to start the computer and use the Recovery Console you require the Windows XP startup disks or the Windows XP CD-ROM.

Note To start the computer from the Windows XP CD-ROM, you must configure the basic input/output system (BIOS) of the computer to start from your CD-ROM drive.

To run the Recovery Console from the Windows XP startup disks or the Windows XP CD-ROM, follow these steps: 1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.

Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted.
2. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3. If you have a dual-boot or multiple-boot computer, select the installation that you must access from the Recovery Console.
4. When you are prompted, type the Administrator password. If the administrator password is blank, just press ENTER.
5. At the command prompt, type the appropriate commands to diagnose and repair your Windows XP installation.

For a list of commands that are available in Recovery Console, type recovery console commands or help at the command prompt, and then press ENTER.

For information about a specific command, type help commandname at the command prompt, and then press ENTER.
6. To exit the Recovery Console and restart the computer, type exit at the command prompt, and then press ENTER.


Method 3: Change the active partition
If the partition marked as active does not contain the Windows XP startup files, or the active partition is an incompatible or a different operating system, you must first mark the correct system partition as active before you restart the computer.

Note There can be only one active system partition at a time.
To mark the correct system partition follow these steps.