help my windows got owerwritten by chromeos

Question

I shrunk my windows and then installed chrome os now I cant boot into windows because it got overwritten

Answer 1

Hi abdurahmon abduroziqov,

I understand this is worrying since Windows was working before and now it no longer boots after installing ChromeOS. The solutions depend on whether the Windows partition still exists, so you need to check that first:

1. Power off the PC completely > Turn it on and enter BIOS:
   1. Press the BIOS/Boot Menu key as the PC brand logo appears.
   2. The common keys are F2, F12, Esc, or Del (often shown on-screen)
2. In the Boot list, look specifically for Windows Boot Manager
   1. If it is present, you can try to boot repair Windows
   2. If it’s not, you may need to reinstall Windows.

A - If Windows Boot Manager exists

• On another PC, follow the guide to Create installation media for Windows 11
• Boot the USB into the affected PC > Select Repair your computer
• Go to Troubleshoot > Advanced options > Startup Repair
• Restart and check if Windows boots normally.
• If Startup Repair fails, boot again from the Windows 11 USB
• Go to Advanced options, but choose Command Prompt
• Run the following commands one by one:
  • bootrec /fixmbr
  • bootrec /fixboot
  • bootrec /rebuildbcd
• Restart and test Windows boot again.

B - If Windows partitions were deleted/overwritten

• Boot from the Windows 11 installation USB like instructed above
• Choose Install now > Select Custom: Install Windows only
• Select the correct drive/partition and install Windows.

Disclaimer: At this point, we have exhausted all troubleshooting and I recommend that we try to perform a clean install to get your computer back into a working condition. Your data on the drive will be clear. You can find instructions on how to perform a clean install by navigating to the bottom of this guide: Reinstall Windows with the installation media - Microsoft Support 

If Windows Boot is no longer present, Windows cannot be restored via settings. At that point, reinstalling Windows is typically the only way to boot Windows again.

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Answer 2

If ChromeOS overwrote the Windows bootloader or system partition, Windows can often be repaired if its partition and files still exist. If the Windows partition was fully deleted or formatted, only a clean reinstall is possible.

To try to repair Windows boot:

1. Create Windows installation media (on another PC if needed) and boot from it (USB/DVD with Windows 10/11). When the Windows Setup screen appears, press Shift + F10 to open Command Prompt.
2. Determine partition style (MBR vs GPT):

      diskpart
      list disk
   

   If the GPT column for your disk has an asterisk *, the disk is GPT; otherwise it is MBR.

      exit
   

3. Find the Windows partition (for both MBR and GPT): In Command Prompt, run:

      dir a:
   

   If no \Windows folder, try:

      dir b:
      dir c:
      dir d:
   

   Continue through the alphabet (skip X: which is the install media) until a drive with a \Windows folder is found. Assume it is C: below; replace C with the correct letter if different.
4. If the disk is MBR: a. Rebuild boot files:

      bcdboot C:\Windows /S C:
   

   Ensure the message Boot files successfully created appears. b. Mark the system volume active:

      diskpart
      list disk
      sel disk C   
      list vol
      sel vol C    
      active
      exit
   

   c. Reboot:

      shutdown -f -r -t 00
   

5. If the disk is GPT: a. Identify the EFI System partition:

      diskpart
      list disk
      sel disk C   
      list part
   

   Look for the partition labeled System. b. Assign a drive letter (example R:) to the System partition:

      sel part <partition-number>
      assign letter=r:
      exit
   

   c. Rebuild the EFI boot files:

      cd /d r:\EFI\Microsoft\Boot\
      ren BCD BCD.bak
      bcdboot C:\Windows /l en-us /s r: /f UEFI
   

   (Replace C with the drive letter where \Windows was found.) d. Reboot:

      shutdown -f -r -t 00
   

If Windows still does not appear or boot after this, it is likely that the Windows partition or its contents were overwritten by the ChromeOS installation. In that case, the only supported option is to back up any remaining data (if accessible from another OS or WinPE) and perform a clean Windows installation using bootable installation media.

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References:

• “An operating system wasn’t found” error when booting Windows
• Boot and install Windows
• Repair the boot menu on a dual-boot PC