Computer turns on but Windows won't boot: what to do
This guide is for anyone whose computer turns on, fans spin and there is a picture, but Windows never reaches the desktop. You will learn to identify where it gets stuck, what to try on your own and in what order, and how not to lose files along the way.
Why does the computer turn on but Windows does not boot?
Because something went wrong in the startup chain: an update that failed partway, corrupted system files, a new driver, or a disk that is starting to fail. The basic hardware works, otherwise there would be no picture at all.
A recent example: according to reports of a Microsoft notice, the Windows 11 security update from 13 January 2026 (KB5074109) caused a limited number of computers not to boot, with the stop code UNMOUNTABLE_BOOT_VOLUME. The suggested way out was to uninstall the update from the recovery environment, exactly like the steps below.
If the computer does not turn on at all, no lights and no fans, you are in the wrong guide. Go to the guide on a computer that will not turn on.
Where exactly does it get stuck?
The point where startup stops says a lot about the cause:
| What you see | Likely cause | What to do yourself | When to come to the lab |
|---|---|---|---|
| A message like “No bootable device” before the Windows logo | The computer does not detect the disk | Unplug external disks and USB drives, restart | If the message comes back: a suspected faulty disk |
| The Windows logo with a spinning circle, endlessly | A stuck update or corrupted system files | Wait, then the recovery environment | If no option in the recovery environment helps |
| “Preparing Automatic Repair” that comes back again and again | Automatic Repair loop | Startup Repair, uninstall the latest update | If the loop continues |
| A screen asking for a BitLocker recovery key | The disk is encrypted, and something in the boot settings changed | Get the key from your Microsoft account | If there is no key anywhere |
| A blue or black screen with a stop code on every boot | Driver, update or disk | Safe Mode, uninstall the update | If Safe Mode does not boot either |
| Reaches the sign-in screen, and after signing in a black screen | User profile or graphics card driver | Safe Mode | If it happens in Safe Mode too |
If a stop code appears, there are details about it in the guide on the Windows blue screen.
The first rule: do your files matter?
If there are files on the computer that matter to you and they have no backup, do not reinstall Windows and do not reset the computer before the files have been saved. That is the most important rule in this guide.
The reason: a reinstall writes large amounts of data to the disk. If the problem is a disk that is starting to fail, every such write could finish it off. Even the Reset this PC option with Keep my files, which is designed to keep files, is not a good bet on a suspect disk.
The actions in the steps below, Startup Repair, uninstalling an update, Safe Mode and System Restore, do not delete documents and photos. A reset and a reinstall are the last step, and only after the files are safe. If they are already inaccessible, the data recovery page explains what can be done. There is no guarantee that everything, or even part, will be recovered, but the odds are better when nothing has been written to the disk first.
How do you get into the Windows Recovery Environment?
The recovery environment is a small system that sits separately from Windows and is designed exactly for this situation. It looks like a light blue screen with the heading Choose an option.
If Windows fails to boot several times, it goes into it on its own. If not:
- Turn on the computer.
- As soon as the Windows or manufacturer logo appears, hold the power button for about ten seconds until the computer turns off.
- Repeat this a second time.
- On the third power-on, according to Microsoft’s explanation of the recovery environment, Windows should boot into the recovery environment. A message about preparing Automatic Repair appears, then a screen with the Advanced options button.
- Click Advanced options, then Troubleshoot and again Advanced options. All the tools are here.
What to try in the recovery environment, and in what order?
From gentle to drastic. After each attempt, let the computer boot and check:
- Startup Repair. Windows checks the startup files and fixes what it can. It does not touch personal files.
- Uninstall Updates. There are two options: Uninstall latest quality update, which is the monthly update, and Uninstall latest feature update, which rolls back a whole version of Windows. Start with the quality update.
- Safe Mode. Startup Settings > Restart, then the 4 or F4 key. If Windows boots in Safe Mode, the problem is almost certainly a driver or a program. This is also a chance to copy important files to an external disk. The details are in Microsoft’s guide to startup settings.
- System Restore. Returns Windows to a point in time when it worked, without touching documents and photos. Works only if restore points were saved.
- Only after the files are safe: Reset this PC, or a clean installation.
What if the recovery environment does not boot either?
Then you enter it from the outside, with a Windows installation USB drive. Prepare it on another computer, with the official tool from the Windows 11 download page on Microsoft’s website. You need an empty USB drive of at least 8GB, because the tool erases everything on it.
- Plug the USB drive into the faulty computer and turn it on.
- In the computer’s boot menu, choose to boot from USB. The key that opens the menu varies between manufacturers, and usually appears briefly on the screen at power-on.
- On the first installation screen, do not click “Install now”. Click Repair your computer at the bottom.
- You reach the same Choose an option screen, with the same tools.
The computer asks for a BitLocker recovery key. Where do you get it?
From another computer or from your phone, at aka.ms/myrecoverykey. Sign in with the Microsoft account of whoever set up the computer, and choose the key whose Key ID matches the one shown on the screen. Comparing the first 8 characters is enough.
Many people are surprised by this screen, because they never turned on encryption. According to Microsoft, on computers that support it, device encryption is turned on automatically when you first sign in with a Microsoft account, and the recovery key is saved to the account.
A few things worth knowing, according to Microsoft’s page on finding your BitLocker key:
- The key is a 48-digit number.
- If the computer is connected to a work or school account, the key is at aka.ms/aadrecoverykey or with the IT department.
- The key may have been printed or saved to a file on a USB drive when encryption was turned on.
- Microsoft support cannot recover a lost key.
If the number keys do not respond on this screen, you can type with the F1 to F10 keys, where F10 is zero. And if the key cannot be found anywhere, the files on that disk are inaccessible. Even a lab cannot read an encrypted disk without the key.
What not to do
- Do not reinstall or reset before the important files have been saved.
- Do not download a “boot repair tool” from unofficial sites. Windows installation tools are downloaded only from Microsoft’s website.
- Do not keep force-shutting down a computer whose disk is clicking or sounds unusual. In that case read the guide on a clicking disk and stop.
- Do not change BIOS settings you are not familiar with. Changing the disk mode or Secure Boot can make things worse and bring up the BitLocker screen.
When to bring the computer to the lab
When the computer does not detect the disk. When no option in the recovery environment helped. When there are important files without a backup and you are not sure how to get them out. And when there are signs of a failing disk: extreme slowness before the failure, clicking sounds or error messages about the disk.
With us, the files are saved first, and only then do we repair. If a clean Windows installation is needed, we back up before, restore the files after, and delete the temporary backup. And next time, a backup before something happens turns a failure like this into an inconvenience instead of a loss.
Did it not work?
The goal is for you to get Windows working again yourself, and in many cases Startup Repair or uninstalling an update is enough. If you have tried everything and the computer still does not boot, we will check whether it is Windows or the disk, and protect the files before anything else. You can start from the Windows reinstallation page.