By Bryce / Last Updated March 10, 2022

The error

“I have a Dell laptop running Windows 10 and it was working well. But suddenly, it failed to boot and with the error “Missing Operating System” appearing. I’m puzzled and I have and have no idea what I should to fix Missing Operating System error in Dell. Is there anyone can offer me some suggestions?”

Analysis of the missing operating system error in Dell

It is common to meet error like “Missing Operating System” or “Operating system not found occurs in Dell. And you might also encounter such error in Lenovo, HP and so on. To fix such issue accordingly and quickly, it is necessary to figure out why operating system is missing. Here are main reasons for “Missing Operating System” error:

  • Inappropriate basic input/output system (BIOS) settings

  • Loose hard drive cable.

  • Damaged Master Boot Record (MBR) on the system hard drive.

  • Windows 10 boot files in system partition are not active anymore.

  • Corrupted system hard drive.

How to fix “Missing operating system” error

If lucky enough, you can settle the issues by quick tricks like restarting computer or remove all external storage devices such as USB flash drive. If the issue is not resolved, you can you can take various effective measures listed below after realizing the causes to “Missing Operating system” in Windows 10.

➢ Way 1. Check cables for the hard drive holds OS
➢ Way 2. Check and adjust the BIOS settings
➢ Way 3. Fix MBR with or without Windows installation disc
➢ Way 4. Set the partition that holds operating system active

Way 1. Check cables for the hard drive holds OS

Windows 10 “Missing Operating System” might happen due to poor connection between computer and the hard drive. In such circumstance, you can check if the SATA cable and power cable for the hard drive is loose or damaged. If so, connected the cables fine or replace it with a good one.

Way 2. Check and adjust the BIOS settings

BIOS tackle with basic setup and boot process. When the hard drive that contains OS is not detected by BIOS, you can found Missing Operating System in Windows 10. Follow the steps given below to check the BIOS settings.

1. Press certain key to access BIOS menu while restating computer. The key could be F1, F10, F12 or Del etc, which can be different in computers made by differential manufacturer.

2. Enter BIOS Setup Utility. Here you can check the Primary IDE Master, Primary IDE Slave, Secondary IDE Master to see whether the hard drive that Windows installed on is detected.

If the system disk is detected, enter Boot menu to ensure that it is set as the first option for booting.

If it is not recognized by BIOS, you can press certain key (that will be presented in the BIOS Setup Utility windows) to reset BIOS settings. After that you can press F10 to save changes and exit from BIOS.

Way 3. Fix MBR with or without Windows installation disc

MBR is on the first sector of the disk, which contains the Partition Table and a small amount executable code for the boot start. If MBR is damaged, you might be prompted by the error “Missing Operating System”. Here offers two methods for you to fix it.

A. Fix MBR with Windows installation disc

If you own Windows installation disc or Windows system repair disc, you can choose this way.

1. Insert the Windows installation disc and boot form it.

2. Navigate to “Repair your computer” >“Troubleshoot” > “Advanced options” >“Command Prompt

3. Type “bootrec /fixmbr” and hit Enter.

PS.:This command also can be used to fix Invalid Partition Table error in Windows 10.

B. Rebuild MBR without Windows installation disc

If you have no Windows installation disc or Windows system repair disc, you can turn to 3rd party freeware – AOMEI Partition Assistant Standard to fix MBR when you are unable to boot your computer. Free download it and have a closer look at how it works:

Download Freeware Win 10/8.1/8/7/XP
Secure Download

Before you do

  • Run AOMEI Partition Assistant and use it to create a bootable media. Then, plug the bootable device into your computer that is unable to boot and boot your computer from it.

  • Or you can unplug the disk that contains Windows system and connect it to a running computer.

Fix corrupted MBR within three steps

Step 1. In the main user interface, click the disk whose MBR need to be repaired and choose “Rebuild MBR”.

Step 2. Choose a MBR typed based on the operating system installed on the disk holding damaged MBR and click “OK”.

Step 3.Here you can review your operation. Confirm it and click “Apply” > “Proceed” to perform it.

After fixing MBR, remove the bootable media and boot your computer from the fixed disk to check whether the error is fixed.

PS.: “Rebuild MBR” will not cause any kind of data loss. It can only solve problems caused by corrupted MBR. It can’t solve problems caused by bootable files or system files missing.

Way 4. Set the partition that holds operating system active

If the partition that Windows installed on is not active, you might also receive error message “Missing Operating System” when starting up your computer. At this time, to fix “Missing Operating System” in Windows 10, you can set the system active via AOMEI Partition Assistant.

Step 1. Boot computer from the bootable media created by AOMEI Partition Assistant and you’ll access the main interface of AOMEI Partition Assistant Standard.

Step 2. Right-click C drive and go to “Advanced” > “Set Active Partition”.

Then, you can do as the prompts given by AOMEI Partition Assistant Standard.

Notes: AOMEI Partition Assistant is featured with many other functions, including copy disk, migrate OS to SSD and so on.


Among all the solutions to fix Missing Operating System in Dell, Lenovo, HP and so on, you can try one or more according to your own specific situation. If you are still unable to boot your computer successfully, you can ask the help of the hard drive manufacturer. If your disk is damaged physically, you might need to replace it with a new one.