Get the fix for “Operating System not found” boot error for Windows XP, Vista, 7, 8, 8.1 or Windows 10.

This error is also very common for Sony VIO laptops, including T-Series ultra books and S-Series.


About “Operating System not found

The following information on this error has been compiled by NeoSmart Technologies, based on the information gathered and reported by our global network of engineers, developers, and technicians or partner organizations.

Description and Symptoms

The error messages, alerts, warnings, and symptoms below are tied to this error.

Symptom 1: “Operating System not found” error screen on startup

When a PC is booting, the BIOS tries to find a operating system on a hard drive to boot from. However, if it is unable to find one, then an “Operating system not found” error is displayed. It may be caused by an error in BIOS configuration, a faulty hard drive, or a damaged Master Boot Record.

Operating system not found error screen

Operating system not found

Another possible error message is “Missing operating system“. This error is also very common on Sony Vaio Laptops.

Causes of this Error

This error has been known to occur as a result of one of the following causes:

Cause 1: Bad BIOS configuration

Since this error occurs when BIOS is unable to find the operating system, checking the BIOS settings first is often a good solution. The BIOS configuration can become incorrect because of power outages, hardware errors or errors made when configuring the BIOS manually.

Cause 2: BCD is damaged

Similar to the errors outlined in the BCD is missing and BCD is corrupt articles, this error can also appear when BCD becomes damaged.

Cause 3: Faulty data cables

If the BIOS is unable to detect the hard drive, the faulty data cables are often to blame. Try to unplug, and then plug them back, or even replace them altogether and see whether the problem persists.

Fixing “Operating system not found” on Windows

Windows Setup CD/DVD Required!
Some of the solutions below require the use of the Microsoft Windows setup CD or DVD. If your PC did not come with a Windows installation disc or if you no longer have your Windows setup media, you can use Easy Recovery Essentials for Windows instead. EasyRE will automatically find and fix many problems, and can also be used to solve this problem with the directions below.

Fix #1: Rebuild BCD via Easy Recovery Essentials

Easy Recovery Essentials’ one-click automated system repair corrects issues caused by corrupt BCD by recreating it from scratch on the active bootable partition. This is done automatically as part of the automated repair process, and requires no manual action or user intervention.
Easy Recovery Essentials can fix many errors such as this automatically using its built-in Automated Repair option. EasyRE is currently available for Windows XP, Vista, 7, 8, Windows 10, and Windows 11 and can be downloaded and created on any PC.

  1. Download Easy Recovery Essentials. Make sure to note your Windows version (XP, Vista, 7, 8, 10, or Windows 11) before you download EasyRE. This guide can help you identify what version of Windows you have installed.
  2. Burn the image. Follow these instructions on how to burn the bootable ISO image very carefully, as making a bootable CD can be tricky! Alternatively, these instructions explain how to create a bootable EasyRE recovery USB stick/drive.
  3. Boot up your PC from the Easy Recovery Essentials CD or USB you created.
  4. Once EasyRE is running, choose the “Automated Repair” option and click Continue.
    EasyRE Home

    Choose “Automated Repair” in Easy Recovery Essentials

  5. After EasyRE scans your computer’s drives, identify and select the drive letter for your Windows installation from the list, and then click on the Automated Repair button to begin.
    EasyRE displays a list of found Windows operating systems

    Choose the drive associated with the Windows installation you’re trying to repair.

  6. Easy Recovery Essentials will start analyzing the selected drive for problems. EasyRE will test for and attempt to automatically correct errors with the disk, partition, bootsector, filesystem, bootloader, and registry. No intervention is required, as EasyRE’s repair is fully automated:
    EasyRE: Automated Repair

    Easy Recovery Essentials searches for errors and makes corrections to the selected Windows installation.

  7. Once the process is complete, EasyRE will report its findings. Click on the Restart button to reboot your PC and test the changes.
  8. The “Operating System not found” error should now be fixed as your PC begins to load:EasyRE: Automated Repair

You can download Easy Recovery Essentials from here.

Fix #2: Change or reset the BIOS configuration

Since this error often occurs when BIOS is unable to find the hard drive, checking BIOS settings might be a good solution.

To check the BIOS settings, follow these steps:

  1. Restart the computer
  2. Press the necessary key to open BIOS menu. This key depends on the computer manufacturer and computer model. This is usually listed on the first screen that appears on the monitor. It can be any of the following: Esc, Del, F2, F8, F10 or F12.
  3. If the screen shows multiple keys, find the key to open “BIOS”, “setup” or “BIOS menu”
  4. Check the BIOS’ main screen to see whether it detects the hard drive, and the boot order to see if it is set correctly.

Here are the screenshot examples of BIOS’ main screen, with a hard drive and a CD-ROM that were properly detected, and a boot order screen that has a hard drive in the first position.

BIOS main settings screen

BIOS main settings screen

BIOS boot order screen

BIOS boot order screen

If the hard drive is not detected properly, consider replacing the data cables, or resetting the BIOS settings to default values. Here are the steps to reset BIOS settings:

  1. Enter the BIOS screen by following the steps outlined above
  2. Find the “Reset to default” or “Setup default” option – it could be either a hotkey, or an option in the menu
  3. Choose the reset option, and answer “Yes” when prompted for a confirmation
  4. Then, select the “Exit -> Exit saving changes” option.
BIOS reset defaults screen

BIOS reset defaults screen

Fix #3: Run Automatic Repair

The Windows Automatic Repair may recover certain boot process related errors in some cases. Here are the steps to access the Automatic Repair from an install disc:

  1. Boot from Windows install disc
  2. Click Next in the setup page after selecting proper language, time and keyboard input
  3. Click Repair your computer and select Troubleshoot
  4. Click on Advanced options
  5. Select Automatic Repair and select your operating system.

Here is an example of what the PC’s startup repair should look like once the BOOTMGR file is properly restored:

Compressed bootmgr fixed

Corrupt bootmgr fixed by Startup Repair

Fix #4: Rebuild the BCD using bootrec.exe

Just as with the BOOTMGR is Missing error, rebuilding your computer’s BCD can fix boot loading issues.

Here are the steps to rebuild the BCD:

  1. Boot from the Windows install disc
  2. Click on Repair your computer after selecting proper language, time and keyboard input.
  3. Select the Windows installation drive, which is usually C:\, and click Next
  4. Choose Command Prompt when the System Recovery Options box appears
  5. Write the following command and press Enter afterwards:
    bootrec /rebuildbcd
  6. If the program finds a Windows installation and asks whether it should add it to the boot list, press Y

Here is an example screenshot of what the PC’s console output should look like once Bootrec is done rebuilding the BCD.

Bootrec utility results screen

Bootrec utility results screen

Fix #5: Reset BIOS settings on Sony VAIO Laptop

The eSupport section of suggests the following solutions if your VAIO laptop is showing this error:

  1. Remove all removable media, e.g. USB flash drives, CDs, DVDs etc.
  2. Reset BIOS settings back to default

Here are the steps to reset VAIO’s BIOS settings if you have Windows XP, Vista, 8 or 8.1:

  1. Remove any peripheral devices you may have connected to the laptop
  2. Restart the computer and press the F2 key when the VAIO logo appears
  3. When the BIOS setup screen appears, press the right arrow key (->) to select the Exit menu section
  4. Select Get Default Values by pressing the down arrow key
  5. Press Enter at “Load Optimized Defaults”
  6. In the Load Optimized Defaults make use of the arrow key to select Yes and then press Enter
  7. Again use the arrow keys to select Exit (Save Configuration) and press Enter

Here are the steps to reset VAIO’s BIOS settings if you have Windows 7:

  1. Press and hold the Assist button after you restarted the laptop until the VAIO black screen appears on the monitor
  2. When the VAIO Care Rescue Mode screen appears use the arrow keys to select Start BIOS setup [F2] and press Enter
  3. Press the F9 key to reset the VAIO’s BIOS to the original default values

In BIOS, make use of the arrow keys to navigate through the screens and options, Enter key to select an option and the ESC key to exit the active window.

More Information

Linked Entries

Support Links

Applicable Systems

This Windows-related knowledgebase article applies to the following operating systems:

  • Windows XP (all editions)
  • Windows Vista (all editions)
  • Windows 7 (all editions)
  • Windows 8 (all editions)
  • Windows 8.1 (all editions)
  • Windows 10 (all editions)

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