A black screen that reads Operating System Not Found or Missing operating system looks like the worst kind of computer problem. Most of the time, it is not.
The message means your PC could not find the small set of files that start Windows. Your documents, photos and installed programs normally sit untouched on the drive while this is happening.
This guide works through the fixes in order, from the two-minute checks to the boot-repair commands, so you try the safe ones first and only reach for the riskier steps if you have to.
“Operating System Not Found” means your PC’s firmware could not find working Windows startup files on the drive it checked. Remove every USB drive, then confirm the correct disk is first in the BIOS/UEFI boot order. If that does not help, boot from Windows installation media and run Startup Repair, then rebuild the boot files with bcdboot on a UEFI PC or bootrec on a legacy BIOS PC.
What “Operating System Not Found” actually means
Windows does not start in one step. Microsoft’s Windows startup troubleshooting reference splits startup into four phases — PreBoot, Windows Boot Manager, Windows OS Loader and the kernel — and lists Operating system missing among the errors that appear when startup stalls in the boot-loader phase.
In plain terms: the firmware handed control to a drive, and the code that should have loaded Windows was not there.
Where that code lives depends on how Windows was installed. On a modern UEFI PC with a GPT disk it is bootmgfw.efi, stored on a small FAT32 EFI system partition. On an older PC using legacy BIOS with an MBR disk it is bootmgr, reached through the disk’s master boot record.
That difference matters more than anything else in this guide. The repair commands for the two are not interchangeable, and running the MBR tools on a UEFI machine will not fix it.
The usual causes are ordinary: a USB stick or memory card the firmware tried to boot from, a boot order changed after a BIOS update or a dead CMOS battery, a loose or failing drive, boot files damaged by an interrupted update or a sudden power cut, or a partition tool that resized or removed the wrong partition.
If your PC shows a specific stop code instead of this message, it may have its own fix — see our guide to error code 0xc0000225.
Try the fixes in this order
Work down the list and stop as soon as Windows boots. The early checks are non-destructive and take only minutes. The later command-line repairs modify boot records, partition settings or the file system, so confirm the correct disk and protect important data before continuing.
Start here: the checks that fix it most often
Remove every USB drive, memory card and external disk
Many PCs try removable media before the internal drive. A USB stick that is not bootable produces exactly this message, and so does a phone left plugged in over USB.
Shut the PC down fully. Unplug USB flash drives, external hard drives, memory cards and phones, then power it on again.
Check the boot order in BIOS/UEFI
Restart and press the setup key shown on the first screen. It varies by manufacturer — Del, F2, F10 and Esc are the common ones.
Open the Boot or Startup section, confirm your Windows drive is listed, and move it to the top. Save and exit.
If your Windows drive does not appear in the firmware, no software fix will help — the PC cannot see the disk. Skip ahead to When the drive itself has failed.
One more firmware setting is worth a look. If the machine was recently switched between UEFI and Legacy/CSM mode, Windows will not start because the firmware is looking for the wrong kind of boot file. Setting it back to the mode Windows was installed in often fixes this on its own.
Reseat the drive and its cables
Shut down, unplug the power cable, and hold the power button for about five seconds to discharge the board. Touch a bare metal part of the case to ground yourself. If the machine is a laptop still under warranty, skip this step rather than risk the warranty.
On a desktop, check that the SATA data and power cables are firmly seated at both the drive and the motherboard, and that neither is visibly damaged. On an M.2 NVMe drive, check that the retaining screw is holding the drive flat in its slot. Reconnect, close the case and try again.
Run Startup Repair from the Windows Recovery Environment
How to reach WinRE when Windows will not start
Windows can put itself into the recovery environment. Microsoft’s Windows RE technical reference documents the triggers: two consecutive failed attempts to start Windows, two unexpected shutdowns or reboots within two minutes of boot completing, a Secure Boot error, or a BitLocker error on a touch-only device.
So if you have already restarted a couple of times and seen a recovery screen, use it — choose Troubleshoot rather than Continue.
If the PC never reaches that screen, you need Windows installation media on a USB drive, made on any working PC. Boot from it, choose your language, then select Repair your computer at the bottom left — not Install now.
Make the USB installer you will need for every remaining fix in this guide.
Run the repair
From the recovery menu choose Troubleshoot → Advanced options → Startup Repair, then pick your Windows installation.
It can take anywhere from a few minutes to half an hour and may restart on its own. Leave it alone until it reports a result.
Startup Repair works on boot configuration only. It does not delete your personal files.
Rebuild the boot files yourself
If Startup Repair reports that it could not repair your PC, you can rebuild the boot files by hand. In the recovery menu choose Troubleshoot → Advanced options → Command Prompt.
First, find out which mode Windows was installed in
Drive letters inside the recovery environment are not the ones you see in Windows. The recovery environment itself usually takes X:, and your Windows volume may not be C:. Start by looking at what is actually there:
diskpart
list disk
list volume
exitMicrosoft’s diskpart list documentation notes that list disk reports whether each disk uses the MBR or GPT partition style. A GPT disk paired with a small FAT32 volume labelled System (usually 100–500 MB) means a UEFI install. An MBR disk with an NTFS System Reserved volume means a legacy BIOS install.
Confirm which letter holds Windows before running anything else. dir C:\Windows should list the usual folders; if it does not, try the other letters from list volume.
UEFI and GPT: rebuild with bcdboot
On a UEFI PC the tool is bcdboot. Microsoft’s bcdboot reference describes what it does: it copies boot-environment files from the installed Windows image to the system partition, creates a fresh BCD store, and on UEFI systems adds a firmware entry in NVRAM pointing at the Windows Boot Manager.
Give the EFI system partition a drive letter first, then run bcdboot against it:
diskpart
list volume
select volume 2
assign letter=S
exit
bcdboot C:\Windows /s S: /f UEFIReplace 2 with the number of the small FAT32 System volume and C: with your Windows letter. The /f switch requires /s, so keep both. Restart once it reports that boot files were created successfully.
Legacy BIOS and MBR: use bootrec
On an older BIOS/MBR install the tool is bootrec. Run the four commands in order:
bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcdThey repair the master boot record, repair the boot sector, scan the disk for Windows installations, and rebuild the boot configuration data. If /rebuildbcd finds an installation and asks whether to add it, press Y. Restart afterwards.
Marking a partition active, and when not to
Older advice for this error is to mark the system partition active in diskpart. It is worth knowing that this applies only to basic MBR disks. There is nothing to mark on a GPT disk, so on a modern UEFI PC the step does nothing at all.
The diskpart active documentation is blunt about the risk: DiskPart only tells the firmware that a partition is a valid system partition, and does not check the contents of that partition. Mark the wrong one and the PC may stop starting altogether. Note which partition was already active before you change anything.
If you have confirmed an MBR disk and want to try it:
diskpart
list disk
select disk 0
list partition
select partition 1
active
exitChoose the small System Reserved partition if there is one, or the Windows partition itself if there is not. Restart to test.
Check the drive for errors
If the drive clicks, disappears from BIOS/UEFI, disconnects, or shows other signs of physical failure, stop here and copy or image your important data to another drive first. chkdsk /f /r writes to the file system and runs an intensive surface scan, which puts extra stress on a drive that is already failing.
Boot files can be intact but unreadable if the file system is damaged. chkdsk is on Microsoft’s list of commands for boot problems. From the recovery Command Prompt:
chkdsk C: /f /rReplace C: with your Windows letter. The /r switch looks for bad sectors and can run for several hours on a large drive. Let it finish — interrupting a repair pass can make things worse.
If it reports a large number of bad sectors, treat the drive as failing rather than as a boot problem to be fixed.
Quick Machine Recovery on Windows 11
Windows 11 has one more option worth trying before you give up. Microsoft describes Quick Machine Recovery as a cloud-based feature that helps devices recover from widespread boot issues by applying fixes delivered through Windows Update when the device enters the recovery environment.
From the recovery menu, choose Troubleshoot → Advanced options → Quick machine recovery, and connect to a network when prompted.
Quick machine recovery targets known, widespread problems, so a one-off local fault usually still needs the manual steps above. Once Windows starts again, check the setting at Settings → System → Recovery → Quick machine recovery.
When the drive itself has failed
Some signs point at hardware rather than software: the drive does not appear in BIOS/UEFI at all, a mechanical hard disk clicks or buzzes, the drive shows up on some restarts and not others, or chkdsk finds heavy bad sectors.
At that point, stop repairing and start rescuing. Every extra hour a failing drive spends powered on is an hour it might not survive.
Remove the drive, connect it to a working PC with a USB adapter or enclosure, and copy your files off before doing anything else. A drive that will not boot will often still let you read from it.
What to try next if files are missing once the drive is readable again.
Common mistakes, and how to avoid a repeat
A few things reliably turn a recoverable problem into a lost weekend.
- Reinstalling Windows first. A clean install removes the boot problem and your files with it. Try the repairs, and copy your data off, before formatting anything.
- Running MBR commands on a UEFI PC. They will not help, and the time spent is time the real fix is not being tried.
- Marking the wrong partition active. See Microsoft’s warning above.
- Deleting the small “System” partition. It looks like wasted space in a partition tool. It is the partition that starts your PC.
- Pulling the plug during an update. An interrupted write to the boot files is one of the most common ways people arrive at this error.
To keep it from happening again: make a Windows recovery USB while the PC is healthy, keep a backup of anything you would miss, let updates finish, and leave the system partitions alone in disk tools.
Frequently Asked Questions
Will I lose my files because of this error?
Usually not. This error is about the files that start Windows, not your documents. Your personal data sits on the Windows partition and is normally untouched. If you are unsure, copy it off before attempting a reinstall.
Is “Missing operating system” the same error?
The two messages come from different code — one from the firmware, one from the boot code on an MBR disk — but the cause and the fixes are the same: the PC could not find working Windows startup files. “No bootable device” usually means the same thing.
Why did this start after a power cut?
A power loss during disk activity can leave boot files half-written. Startup Repair, or a rebuild with bcdboot or bootrec, usually puts it right.
Do I need Windows installation media?
For Startup Repair and every command in this guide, yes — unless the PC still reaches the recovery environment on its own after two failed starts. Making the USB takes a few minutes on any working PC.
Do these steps work on Windows 10 as well as Windows 11?
Yes. The recovery environment, bootrec, bcdboot and chkdsk work the same way on both. Only Quick Machine Recovery is Windows 11 only. If you are still on Windows 10, it is worth knowing how long security updates continue.
Getting back into Windows
“Operating System Not Found” is a startup problem far more often than a disaster. The order matters: remove the USB drives, check the boot order, run Startup Repair, and only then rebuild the boot files with the tool that matches your firmware.
If the drive has stopped appearing in BIOS altogether, change tack and rescue the data instead of trying to repair the boot.
Once Windows starts again, make a recovery USB while everything is working. It turns this whole article into a fifteen-minute job next time.
