Windows won’t start

Windows disappears or won't boot after a BIOS update

After updating the computer's BIOS/UEFI firmware, Windows no longer appears as a boot option, or the PC fails to start, even though the update seemed to complete successfully.

Difficulty
Advanced
Time
30–90 minutes
DIY cost
$0
Pro cost
$100–$220

Symptoms

  • Boot problems started immediately after a BIOS update
  • Windows drive may or may not still be listed in BIOS boot order
  • PC may show no bootable device or a Secure Boot related error
  • Previously boot mode setting (UEFI/Legacy) may have reset to default

Likely causes

  • CommonBIOS update reset boot mode from UEFI to Legacy or vice versaFirmware updates sometimes reset settings to factory defaults, breaking compatibility with how Windows was installed.
  • CommonSecure Boot re-enabled or its keys reset by the updateThis can block a boot loader that isn't set up to match the new Secure Boot state.
  • PossibleBoot order reset, no longer pointing to the Windows driveFirmware updates commonly reset the boot priority list.
  • PossibleUpdate itself failed or was interruptedAn incomplete BIOS flash can leave the firmware in an unstable state affecting storage detection.
  • Less commonCSM (Compatibility Support Module) setting changedThis legacy compatibility setting affects how older Windows installs are recognized.

What to do

  1. Enter BIOS/UEFI setup and check the Boot Mode setting; if Windows was installed in UEFI mode, make sure UEFI mode is selected rather than Legacy/CSM.
  2. Check the boot order list and manually add or re-select the Windows drive if it's not listed first, or use the 'Add boot option' feature if available to point to the correct EFI boot file.
  3. If Secure Boot is enabled and causing a violation error, test with Secure Boot temporarily disabled to confirm it's the cause, then address compatibility properly rather than leaving it off long-term.
  4. Load 'optimized defaults' cautiously, then manually reapply the correct Boot Mode and boot order settings rather than assuming defaults match your original setup.
  5. If the drive isn't detected at all after the update, check whether the update changed the storage controller mode (AHCI/RAID) and try reverting it.
  6. Boot from a Windows installation USB and use 'bootrec /rebuildbcd' if Windows files are found but not bootable.
  7. If the BIOS update seems to have failed or is behaving very unpredictably, check the manufacturer's site for a firmware recovery procedure specific to your model.

Tools and parts

  • Bootable Windows installation USB drive

When to call a pro

If adjusting boot mode, Secure Boot, and boot order doesn't restore Windows after a BIOS update, a technician familiar with firmware recovery can help avoid further complications.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.