Operating System Not Found: How To Recover A Missing Operating System

Not being able to boot your operating system is far from ideal. If you have a Dell, Lenovo, Sony, Acer, or HP laptop, and are running into an error saying ‘Operating System Not Found’ you are not alone. This error is common by these laptop manufacturers, but there are solutions available to get you back up and running. Windows 10 seems especially susceptible, but this error can occur in other versions of Windows.

What does the Operating System Not Found error mean?

Your computer may have been running poorly, even freezing or crashing. Then an error message presents itself splashed onto a black screen upon trying to start your system. This is because your hard drive is attempting to boot into the Windows operating system, but is encountering a problem.

Your hard drive is your main storage device for your computer. The hard drive has to be undamaged, formatted and partitioned correctly, and properly able to interface with the BIOS or problems like the the “Missing operating system” or “Operating system not found” can arise.

Remember that the hard drive must have an operating system preinstalled. If this is a new hard drive, you’ll need to install Windows onto it first before attempting to boot. Unplug any external storage, such as flash drives or secondary hard drives. These can create problems when the main hard drive is trying to interface with the BIOS.

What do you see on the screen when this error occurs?

The error will display one of the following two messages:

  • Operating system not found
  • Missing Operating System
Operating System not found error message
Missing operating system error message

What causes the “Missing operating system” or “Operating system not found” error?

There are a few things that could be triggering the “Operating System not found” or “Missing operating system” error. It’s important to recognize that the BIOS, MBR, and hard drive need to be able to interact correctly to find and boot Windows 10. If one of those is damaged, corrupt, or has incorrect settings, the system may fail to boot. All the below causes, can be traced back to this central idea.

BIOS not detecting hard drive

BIOS is a software responsible for communicating basic functions to the hardware, most critically booting, but also using peripherals and hardware identification. BIOS stands for Basic Input Output System and the software is stored in a small chip on your motherboard. Sometimes there are problems when the BIOS is attempting to interface with the hard drive for booting, which can cause this error. If BIOS settings are messed up, BIOS may fail to detect the hard disk.

Failing hard drive

Hard drives don’t last forever. If your hard drive is over three years old, you’ll want to watch for signs that it is beginning to fail. Weird scratching or clicking noises coming from your hard drive should be especially alarming. Increasing frequency of crashes, problems moving files, and slow responses while searching through files are also indicative of a problem. Backing the hard drive up and replacing it before it fails is always preferred. If the hard drive begins to go, this error can crop up.

Signs to remember:

  • 3+ years old
  • Scratching or clicking noises
  • Increasing frequency of crashes
  • Long time to access files
  • Folders or files missing

Master Boot Record is malformed in sector 0

The Master Boot Record (MBR) is vital and should be the first sector partitioned on your hard drive. This is sector 0. If for some reason, the MBR has become corrupt or malformed, the instructions for how and where to boot the operating system will be unavailable to the BIOS. The MBR has three major sections: the master boot code, the master partition table, and the disk signature. The boot code identifies the BIOS, the system partition, which then can initiate the boot sector.

Ultimately if your MBR is corrupt, it needs to be fixed to load your operating system and get past this error.

Incompatible partition active

By default, the partition that Windows 10 is loaded on, is set as active. It is possible to accidentally select another partition on your hard drive and set it to active. If you do that, the Windows operating system partition will be marked inactive. When you restart your computer, the system will not be able to find Windows 10, and you’ll experience the Operating System Not Found error.

If an incompatible partition is active, you will need to mark the correct partition as active.

MBR within Inactive Partition

Similarly, if MBR is located within a partition that has been marked inactive, the data the BIOS needs to find and boot Windows 10 is inaccessible. Changing the partition to active is likely to solve the problem.

5 proven solutions to fix the “Missing operating system” or “Operating system not found” error

Below are 5 tested methods, organized from simplest to complex. Follow through to find a solution to recover your missing operating system!

Note: Microsoft recommends contacting the manufacturer of your hard drive if you are having continued issues after basic troubleshooting. A manufacturer often has specific utility tools for their hard drives, that will better troubleshoot damage or corrupt areas. The manufacturer can also confirm the appropriate BIOS settings.

1. Confirm that BIOS can detect the hard drive

You will start by making sure there isn’t a problem between the hard drive and BIOS.

  1. As you press the Power button to turn on your computer, press and hold F10, F2, F12, F1, or DEL to enter the BIOS. Unfortunately this varies depending on the machine. This key is set by the manufacturer. Below is a list of the most common BIOS hotkeys to use, by brand: 
    • Acer: F2 or DEL
    • ASUS: F2 for all PCs, F2 or DEL for motherboards
    • Dell: F2 or F12
    • HP: ESC or F10
    • Lenovo: F2 or Fn + F2
    • Lenovo (Desktops): F1
    • Lenovo (ThinkPads): Enter + F1
    • MSI: DEL for motherboards and PCs
    • Microsoft Surface Tablets: Press and hold volume up button.
    • Origin PC: F2
    • Samsung: F2
    • Sony: F1, F2, or F3
    • Toshiba: F2
  2. When the BIOS Setup Utility is displayed, you can then release the hotkey.
BIOS home screen
  1. Within BIOS look for IDE Primary Master, IDE Primary Slave, and IDE Secondary Master. At least one of these needs to display a disk name. This step is why it’s important to remove all external hard drives first. If one is displayed, exit the BIOS.
  2. If all three, display None/Not Detected, the BIOS is not detecting any hard disk.
  3. You can select None or Auto at this point and leave the BIOS.

2. Check the health of the hard drive

Since you can’t boot your computer, you can’t use the standard hard drive diagnostic tool included in Windows, chkdsk. Instead, you want to boot back into BIOS and test the hard drive there.

  1. Enter the BIOS with the same method and hotkey that you used in the previous solution.
  2. Within the BIOS Setup Utility, use the arrow keys to select the Tools menu.
  3. Select Hard Drive Self Test and press Enter.
BIOS hard drive self test
  1. Wait for the test to complete. This may take some time.

If the hard drive passes all the tests, then your hard drive is healthy and the problem lies elsewhere. But if your hard drive fails any test, you have two options. You can contact your manufacturer about a replacement hard drive, if you are still under warranty. Or you can research and purchase a new and improved hard drive.

Remember that hard drives fail eventually, and sometimes they just need to be replaced.

3. Set BIOS to default settings

Somehow the settings of the BIOS may have changed or been tampered with unknowingly. Incorrect BIOS settings can trigger the ‘Operating System Not Found’ error when trying to boot Windows. You may solve the problem by reverting the BIOS settings to default.

  1. Enter the BIOS with the same method and hotkey that you used in the first solution.
  2. Within the BIOS Setup Utility, look for the default settings option. Usually it will include the word default and may be listed as:
    • Get Default Values
    • Load Optimal Defaults
    • Load Optimized Defaults
    • Load Setup Defaults
Reset BIOS configuration to default
  1. Save the default settings by pressing F10 and exiting the BIOS.
  2. Restart the computer and see if it will boot correctly. If not, continue to the next solution.

4. Repair the Master Boot Record (MBR)

Since the computer won’t boot you are limited in your troubleshooting options. Thankfully you can access the command prompt within the Windows repair settings. Using this you will rebuild the boot file and fix the master boot record. This method also allows you to complete this process without using installation media, which you may or may not have.

Warning: Microsoft recommends running antivirus software before using this command. If a virus is present in the system, this command could damage the partition table by creating inaccessible partitions. As always, any hard drive work should be backed up first.

To repair the master boot record:

  1. Press the Start button for the computer and immediately start pressing Ctrl + Alt + Del.
  2. This will force the system to restart. Press Ctrl + Alt + Del again.
  3. Windows will flash a message about Preparing automatic repair, Diagnose, Attempting Repairs.
Preparing Automatic Repair
  1. Select Advanced options and then Troubleshoot.
  2. Select Advanced options again and then select Command Prompt.
  1. In the Command Prompt window, enter “bootrec.exe /rebuildbcd
  2. When that completes, enter “bootrec.exe /fixmbr
bootrec.exe /fixmbr
  1. Finally, enter “bootrec.exe /fixboot
  2. Check to see if the problem is fixed.

5. Set the correct partition active

Now that the MBR has been repaired you can use the Command Prompt again to navigate to the correct partition and mark it as active. This will solve the problem of the wrong partition being marked.

  1. Repeat steps 1 through 5 from solution 4 to open the Command Prompt in the Windows Recovery Environment.
  2. In the Command Prompt window, enter “diskpart
  3. Then type “list disk” and hit Enter. There will be a list of hard drives currently attached to the computer.
  4. You should have only one hard drive if you follow earlier instructions so, type “select disk 0” and press Enter.
  5. Type “list partition” to now retrieve a list of all partitions on that hard drive disk.
  6. You want to select the partition with MBR. This will be entered as “select partition [n]“, where [n] is the correct MBR partition number for your system.
  7. Now you are working within the correct disk and partition, to mark it as active, just type “active” and press Enter.
  8. Exit the Command Prompt and restart the computer.


The solutions listed above are the most effective for solving the ‘Operating System Not Found’ or ‘Missing Operating System’ boot error. You will either need to reset your BIOS settings, repair or rebuild your MBR, change the active partition, or replace your hard drive. Thankfully, none of these solutions are very difficult.

If your hard drive is failing, make sure to research before buying a new hard drive. If you’ve had a hard disk drive (HDD) and are able to upgrade to the new, faster, and better performing solid state drives (SSD) it is highly recommended. They aren’t significantly more expensive, but the user experience is definitely an upgrade.

Hopefully with this guide, you are back up and running in no time!

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