Operating System Not Found

When you try to start a Windows based computer, you may receive an error message that reads

“Operating System Not Found” or “Missing Operating System”. Do you have any idea why you get this

information and how can you solve this issue?

Why Operating System Not Found:

“Missing Operating System” may occur if one or more of the following accidents happen:
Possible reason 1: system damage.
Corresponding solutions: there is no better way for you but to reinstall the operating system.
Possible reason 2: The hard disk is damaged so that the BIOS (basic input/output

system) does not detect the hard disk.
Corresponding solutions: Fix or replace your hardware if the hard disk is damaged. Contact the

manufacturer of your hard disk to find a utility that you can use to perform a detailed scan for

damaged areas of the disk. However, the damage to your hard disk may be serious. Sometimes the

only solution is to replace your hard disk.
If the hard disk failure is eliminated, you should consider whether the BIOS setting goes wrong.

Verify the computer’s BIOS settings to make sure that BIOS lists is correct and the hard disk can

be detected. After that, restart the computer, and then test to determine whether the issue is

Possible reason 3: MBR (master boot record) is incorrect or corrupted.
Corresponding solutions: Use fixmbr command to repair the MBR of the startup partition. Before

using this command, you need to use a bootable disk to run antivirus software, because this

command can damage your partition table if a virus is present. If the fixmbr command detects an

invalid or non-standard partition table signature, it will prompt you for permission to rewrite

the MBR.
Possible reason 4: The partition that contains the MBR is no longer active. An

unmatched partition is marked as Active.
Corresponding solutions: If all solutions above do not work, check whether the partition that

contains the MBR is no longer active, and an unmatched partition is marked as Active. Then you

need to set the partition that contains the MBR active.
Note: Usually, there is only one active partition in a MBR hard drive. An active partition can

be any primary partition, other than logical partition. Please ensure that the partition you are

about to mark active includes valid system files, otherwise the disk will not start.

Three Approaches to Mark A Partition as Active

Approach 1: Use Windows GUI (requires Windows Pre-installation Environment)
1. Run “compmgmt.msc” or right click “My Computer” and click “Manage”.
2. In the control panel, choose “Computer Management”-“Storage”-“Disk Management”;
3. Right click the partition you want to set, and click “Mark Partition as Active”.
Note: You can change the active partition by mark another one as active (please make sure it

includes valid system files). However, Disk Management doesn’t provide users with a direct option

to remove the active property.
Approach 2: Use diskpart command (requires Windows Pre-installation Environment)
1. Set active:
Run “cmd” – “diskpart” – “list disk” – “select disk x” – “list partition” – “select partition x” –

“active” – “exit”.
2. Remove active:
Run “cmd” – “diskpart” – “list disk” – “select disk x” – “list partition” – “select partition x” –

“inactive” – “exit”.
Note: Depending on your disk layout, “x” can be “0”, “1”, “2”…

Approach 3: Use MiniTool Partition Wizard Bootable CD
MiniTool Partition Wizard Bootable CD can help you to boot computer from MiniTool Partition Wizard

Free to set a partition active/inactive. Here is the tutorial.
Step 1. Download the iso file of MiniTool Partition Wizard

Bootable DC.
Step 2. Burn the iso file to a USB flash drive or CD/DVD Disc.
Reference: How to Build Free Bootable Partition Manager with

Step 3. Set your computer to boot from this bootable media.
Connect the bootable media with your computer, and then boot your computer into BIOS. Now set to

boot from the bootable device and save your change.
Note: If you are using a CD/DVD disc, you need to boot your computer firstly. Otherwise, you

cannot place the disc into CD-ROM. After that, you can set the computer to boot from CD-ROM


Then you will see the welcome page of MiniTool Partition Wizard.
Step 4. Now you can check whether the partition that includes valid system files has been set

active. If not, right click the partition and select “Set Active“.


But if you find an unmatched partition is marked as active, you can also set it inactive.

And finally, don’t forget to click “Apply“.
You can see from the software interface that this free software is user-friendly and ease of use.

Still, there are many useful features like copy partition, wipe partition, etc. for you to apply.

So by contrast, approach 3 is more outstanding.
In conclusion, “Operating System Not found” can be caused by various factors. For each factor,

there is a corresponding solution. Now share this post to help more users to deal with “Missing

operating System”.


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