"Boot device not found" and "No bootable device"

The computer switched on but could not find a disk with Windows on it. Either it is looking in the wrong place, or the disk is not answering.

What you seeBoot Device Not Found (3F0) / No bootable device / Operating System not found / Reboot and select proper boot device

What it means

Before Windows starts, a small program built into the computer (the BIOS, or UEFI) looks for a disk to start from. This message is from that program, not from Windows. It means one of three things:

1. it tried the wrong device, such as a USB stick left in a port;
2. its settings were changed or lost, so it no longer knows where Windows is;
3. the disk itself is disconnected, damaged or dead.

Quick checks

1. Remove all USB drives, memory cards and discs, then restart. This alone fixes many cases.
2. Switch off fully (hold the power button ten seconds), wait, and start again. A disk that is slow to wake may answer the second time.
3. On a desktop, check that nothing was knocked: a loose data or power cable to the disk gives this error.

Check the BIOS settings

1. Switch on and at once tap the set-up key repeatedly. It is shown briefly on screen: usually F2, F10, Del or Esc, depending on the maker.
2. Find the storage or information page. Is your disk listed by name? (for example a model number with "SSD" or "NVMe"). - Listed: the disk is alive. Go to step 3. - Not listed: the computer cannot see the disk. Go to "If the disk is not detected".
3. Open the Boot page. The first boot device should be Windows Boot Manager or your internal disk. Move it to the top if it is not.
4. Look for a Load defaults or Restore defaults option (often F9), apply it, then Save and exit (often F10). A flat clock battery on an old computer makes it forget its settings; if the date and time are also wrong at every start, that small coin battery needs replacing.

Do not change settings you do not recognise, and in particular do not switch between "UEFI" and "Legacy/CSM" modes or the storage mode (AHCI/RAID) unless you are reversing a change that caused the trouble.

If the disk is detected but Windows does not start

The start-up files are damaged. You need the Windows recovery environment:

• Start the computer and interrupt it three times with the power button as it tries to load, or
• start from a Windows installation USB stick and choose Repair your computer.

Then Troubleshoot › Advanced options › Startup Repair. If that fails, follow automatic repair loop, which lists the commands to rebuild the start-up records.

If the disk is not detected

• Desktop: switch off and unplug. Reseat both cables on the disk, try another data cable and another port on the board.
• Laptop: an M.2 SSD can work loose after a fall. If you are comfortable opening the base, reseat it and tighten its screw. Otherwise go to a service centre.
• Many makers have a built-in hardware test, started with a key such as F2, F12 or Esc at power-on. Run the disk test. A failed test with an error code is what the warranty desk will ask for.

A disk that is not detected after reseating has usually failed. Windows can be reinstalled on a new SSD in an hour; the files on the old disk are another matter.

About your files

If the disk is detected, your files are almost certainly intact; do not reset or reinstall before trying to copy them (see automatic repair loop for the Notepad method). If the disk has failed and holds files with no backup, stop trying to start it and consult a data recovery service; repeated attempts can make recovery harder.

For Windows 11 and Windows 10. Written in November 2026. Menus move between updates; use the search box in Settings if a name differs. Back up important files before any step that resets, repairs a disk or opens the computer. This is an independent guide, not connected with Microsoft.