What does 'Operating system not found' mean?

The short answer

Your computer can’t find or load the operating system (like Windows) it needs to start, so it gets stuck at a black screen with an error message.

Why does it happen?

When you turn on your computer, it looks for an operating system on your hard drive or SSD. If it can’t find one, you’ll see this error. Common causes include:

  • Your boot order is wrong — the computer is trying to start from a USB drive or DVD instead of your main drive
  • A loose or disconnected drive cable — the physical connection between your hard drive and the motherboard came loose
  • A corrupted boot record — the small piece of data that tells your computer where to find the operating system got damaged
  • A failing or dead hard drive — the drive itself has stopped working
  • A missing operating system — the drive was wiped, formatted, or never had one installed

How to fix it

Work through these steps in order:

  1. Remove USB drives and discs — unplug any USB sticks, external drives, or CDs/DVDs and restart
  2. Check the boot order in BIOS — press F2, F12, or Delete during startup to enter BIOS, then make sure your main hard drive is listed first under boot priority
  3. Reseat the drive cable — open your computer and firmly reconnect the SATA or power cable going to your hard drive
  4. Run startup repair — boot from a Windows installation USB and choose “Repair your computer” then “Startup Repair”
  5. Rebuild the boot record — from the Windows recovery command prompt, run bootrec /fixmbr and bootrec /rebuildbcd
  6. Test the hard drive — use your computer manufacturer’s built-in diagnostics (usually accessible from BIOS) to check if the drive is failing

When should you worry?

If unplugging a USB drive or fixing the boot order solves it, you’re fine. But if the error keeps coming back:

  • Your hard drive may be dying — back up your data as soon as possible and consider replacing it
  • Your operating system may need reinstalling — a corrupted installation sometimes can’t be repaired
  • Your motherboard could have an issue — if it can’t detect any drive at all, the problem may be deeper than software