Windows boot failure questions appear consistently on the A+ Core 2 exam. The exam presents a specific error message or symptom and asks you to identify the cause or the correct repair tool. Knowing the Windows boot process helps you work backwards from any symptom.
The Windows Boot Sequence
- POST — Hardware initialisation by BIOS/UEFI
- Boot device selection — BIOS/UEFI reads the boot order and finds the boot device
- MBR/GPT — Master Boot Record (legacy BIOS) or GPT partition table (UEFI) is read
- Boot Manager —
bootmgr(BIOS) orbootmgfw.efi(UEFI) loads - BCD — Boot Configuration Data is read to find the OS to load
- Windows Loader —
winload.exeloads the Windows kernel - Kernel and drivers — Kernel initialises, hardware drivers load
- Session Manager — Windows completes startup
Error: "BOOTMGR is missing"
This error appears when the system can read the disk but cannot find the boot manager file.
Cause: the boot partition is missing, corrupted, or the active partition is set incorrectly.
Fix using Windows Recovery Environment (WinRE):
- Boot from Windows installation media
- Select "Repair your computer" → Command Prompt
- Run
bootrec /fixmbr— Rewrites the Master Boot Record - Run
bootrec /fixboot— Rewrites the boot sector - Run
bootrec /rebuildbcd— Scans for Windows installations and rebuilds the BCD store
Error: "Boot Configuration Data file is missing"
This error means the BCD store itself is missing or corrupted.
Fix: bootrec /rebuildbcd — This scans all disks for Windows installations and adds them to a new BCD store.
Alternative: bcdedit — A command-line tool for manually viewing and editing BCD entries. Used when you need to change boot settings, add an OS, or fix specific BCD entries.
The difference: bootrec fixes and rebuilds. bcdedit views and edits individual entries.
Startup Repair
Startup Repair is the automated recovery tool built into WinRE. It diagnoses and fixes common boot problems without requiring manual command input:
- Checks file system integrity
- Repairs corrupted boot files
- Fixes BCD issues
How to access WinRE:
- Interrupt boot three times (Windows 10/11 will automatically enter WinRE)
- Boot from Windows installation media → Repair your computer
- F8 during boot (in some configurations) → Advanced options
Safe Mode
Safe Mode loads Windows with only essential drivers and services. It is used when Windows starts but is unstable:
- Safe Mode: minimal drivers, no networking
- Safe Mode with Networking: adds network drivers for downloading updates or tools
- Safe Mode with Command Prompt: text-only interface
How to enter Safe Mode in Windows 10/11:
- From WinRE: Troubleshoot → Advanced options → Startup Settings → Restart → press 4, 5, or 6
- From a running Windows: msconfig → Boot tab → Safe boot checkbox → Restart
Exam tip: if the question says Windows cannot start normally but you can reach Safe Mode, the problem is with a driver or non-essential service. Start by disabling recently installed drivers.
System File Checker
sfc /scannow — Scans all protected system files and replaces corrupted ones from the Windows cache.
Run from an elevated command prompt. If Windows cannot start, run from WinRE:
sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
DISM
DISM /Online /Cleanup-Image /RestoreHealth — Uses Windows Update to download and replace corrupted system files. Used when SFC finds problems it cannot fix from the local cache.
The order: run SFC first. If it fails, run DISM to repair the component store, then run SFC again.
Exam Question Patterns
"Windows displays 'BOOTMGR is missing' at startup. Which command repairs this?" — bootrec /fixmbr and bootrec /fixboot
"Windows fails to boot. Which tool automatically diagnoses and repairs common startup problems?" — Startup Repair
"A technician needs to manually edit the Windows boot configuration." — bcdedit
Practice A+ Windows troubleshooting questions to build pattern recognition for boot error scenarios.
WinRE Access Methods — All Four Ways the Exam Tests
Windows Recovery Environment (WinRE) is where you run boot repair tools. Knowing how to get there is tested explicitly.
Method 1 — Three-interrupt method (automatic): In Windows 10 and 11, if Windows fails to boot successfully three times in a row, it automatically enters WinRE on the fourth boot attempt. This is the method that works when you have no installation media and cannot access settings. Technicians sometimes use this deliberately by holding the power button during the Windows loading screen — interrupt the boot twice, and on the third failed boot Windows offers to enter recovery.
Method 2 — Boot from installation media: Insert a Windows installation USB or DVD, boot from it (change boot order in BIOS/UEFI), and select "Repair your computer" instead of "Install now." This is the most reliable access method because it does not depend on the existing installation being partially functional. Keep a bootable Windows 10/11 USB ready.
Method 3 — Recovery partition: Most OEM computers (Dell, HP, Lenovo) include a recovery partition that contains WinRE tools. Access varies by manufacturer — often F11 or F12 at boot, before Windows starts loading. This method works when the operating system installation is corrupted but the recovery partition is intact.
Method 4 — F8 / Shift+F8 (legacy): In Windows 7, F8 during early boot brought up the Advanced Boot Options menu (including Safe Mode). In Windows 10/11, the fast boot UEFI implementation makes this unreliable — Windows loads too quickly for the keystroke to register. Shift+F8 sometimes works on systems without UEFI fast boot. The reliable modern alternative is holding Shift while clicking Restart from the Windows Start menu.
Exam trap: A question asks "how can a technician access WinRE on a Windows 11 computer that cannot start?" The safest answer is booting from installation media. The three-interrupt method is also correct but assumes you can interrupt the boot three times (possible if the system gets partway through boot before failing).
The Specific bootrec Commands and What Each Does
All four bootrec commands get tested. The distinctions between them matter.
bootrec /fixmbr: Writes a new Master Boot Record to the system disk. The MBR is the first 512 bytes of the disk and contains the bootstrap code that begins the boot process. Does NOT modify the partition table. Use when: MBR is corrupted, overwritten by a bootloader from another OS (Linux dual-boot), or infected by an MBR-level boot sector virus.
bootrec /fixboot: Writes a new boot sector to the active partition. Different from the MBR — the boot sector is at the beginning of the partition (not the disk) and contains code that loads bootmgr. Use when: the partition's boot sector is corrupted or was overwritten.
bootrec /rebuildbcd: Scans all disks for Windows installations, then offers to add them to the BCD store. This is the command for when the BCD is missing or corrupted, or when you have a Windows installation that Windows is not aware of (it was removed from the BCD but the files still exist). The rebuild process prompts you to confirm adding each found installation.
bootrec /scanos: Scans all disks for Windows installations and displays a count, but does NOT make any changes. This is a diagnostic-only command. Use /scanos first to confirm that your Windows installation is detected before running /rebuildbcd. If /scanos reports "0 Windows installations found," the problem is not with the BCD — the Windows installation files themselves may be corrupted or missing.
The critical distinction between /fixmbr and /fixboot: /fixmbr fixes the disk-level MBR code. /fixboot fixes the partition-level boot sector code. Both are needed when the full boot path is corrupted. The error message gives you a clue: "BOOTMGR is missing" = boot sector issue (/fixboot). No output at all after POST = MBR issue (/fixmbr).
System Restore — How It Works and When It Fails
Volume Shadow Copy Service (VSS): System Restore relies on VSS to create restore points. VSS snapshots the state of protected volumes at a point in time. These snapshots are stored on the same volume (in a hidden area) and can be used to restore the system to that prior state.
What System Restore restores:
- System files and Windows registry
- Installed programs and drivers
- Windows settings
What System Restore does NOT restore:
- User data files (documents, photos, downloads) — these are not touched in either direction
- Email data stored outside the system files
- Files excluded from Volume Shadow Copy
When System Restore will not help:
- Hardware failure: System Restore restores software state. A failing hard drive, bad RAM, or dead power supply is not fixed by restoring to a previous software state. If the hardware is failing, the restored system will fail too.
- Corrupted VSS store: If the Volume Shadow Copy service is disabled or the shadow copies have been deleted (malware often deletes shadow copies — ransomware does this specifically to prevent recovery), no restore points exist.
- Disk full: If the drive is completely full, VSS cannot create snapshots. Check that the System Protection settings allocate enough disk space for shadow copies (Settings → System Properties → System Protection → Configure → Max Usage).
- Malware deleted restore points: Run vssadmin list shadows to check if restore points exist. If ransomware has been present, they are likely gone.
UEFI Secure Boot Issues — The Modern Failure Mode
Secure Boot is a UEFI feature that validates the digital signature of the bootloader before executing it. It ensures that only trusted software boots the system, preventing bootkit malware from loading before the OS.
When Secure Boot causes problems:
- Installing Linux: Many Linux distributions now have signed bootloaders and work with Secure Boot. Older distributions or custom kernels may not be signed and will refuse to boot.
- Boot from unsigned USB: A WinRE USB or other bootable media created with older tools may not have a signature that Secure Boot recognises. The system refuses to boot from it.
- After BIOS update: Some BIOS updates change Secure Boot key databases, which can cause previously working systems or operating systems to fail to boot.
- Unsigned drivers: In some configurations, Secure Boot requires that even kernel drivers be signed. Custom or unsigned drivers may cause a failure.
Symptoms: A Secure Boot error appears as text on screen (varies by manufacturer but typically mentions "Secure Boot" or "Unauthorized changes to UEFI Secure Boot"), or the system simply falls back to the boot device selection screen without booting from the expected device.
How to disable Secure Boot temporarily for troubleshooting:
- Enter UEFI/BIOS settings at boot (typically Del, F2, or F10 — varies by manufacturer)
- Navigate to the Security or Boot tab
- Find Secure Boot setting
- Change to Disabled
- Save and exit
Re-enable Secure Boot after resolving the issue. Running with Secure Boot disabled exposes the system to bootkit threats.
Exam tip: If a question describes a system that worked fine until a new Linux distribution was installed, and now it will not boot, the cause is Secure Boot blocking the unsigned or differently-signed bootloader. The fix is to either enroll the Linux distribution's signing key or temporarily disable Secure Boot.
Recovery Partition vs Installation Media — When Each Is Required
Recovery partition:
- Contains WinRE tools and often a factory reset image
- Located on the same physical drive as Windows
- Accessible even without external media
- Limitation: If the drive itself has failed or is physically damaged, the recovery partition cannot be accessed. Also, if the recovery partition was deleted (common when OEM computers are custom imaged), it may not exist.
- Use it when: The Windows installation is corrupted but the drive is healthy.
Installation media (USB/DVD):
- Independent of the system drive
- Contains WinRE regardless of the installed OS state
- Works even if the system drive has failed
- Required when: the recovery partition does not exist, the drive has failed or is being replaced, you need to reinstall from scratch.
- Use it when: You need guaranteed access to recovery tools regardless of local drive state.
Exam scenario: "A technician finds that a workstation's drive has completely failed and needs to be replaced. After installing the new drive, what is needed to install Windows?" Installation media — there is no recovery partition on a new, blank drive.
Checklist for First Five Minutes of Boot Failure Troubleshooting
A structured approach that covers the most common causes quickly.
1. Is the system getting power? Check power light, fan spin, any POST indicators. If nothing at all: power supply, power cable, power button.
2. Does the system POST? If you hear POST beeps or see the manufacturer logo but it fails afterward: the hardware is alive, the problem is in the boot sequence.
3. What does the error message say? "BOOTMGR is missing" → boot sector or MBR issue, use bootrec. "Boot device not found" → BIOS/UEFI cannot find any bootable device, check boot order and drive detection. No error, endless reboot → possible driver issue, try Safe Mode.
4. Can you access Safe Mode? If yes: the core OS can load. The problem is likely a driver, service, or recently installed software. Disable recently added drivers or use System Restore.
5. Can you access WinRE? Try the three-interrupt method or boot from installation media. If you can reach WinRE, run Startup Repair first — it is automated and catches most common problems. If Startup Repair fails, move to manual bootrec commands.
6. Is the drive detected? In BIOS/UEFI setup, check if the drive appears. If it does not: cable connection (SATA cable or M.2 seating), drive failure. Try a different port or cable before concluding drive failure.
7. Is this a hardware problem? If the OS is restored and still fails, if the error is intermittent, if the system is unstable even in safe mode — suspect hardware. Run memory diagnostics (Windows Memory Diagnostic) and disk health checks (SMART data via a tool like CrystalDiskInfo).