Section 11: Boot Failures

The Big Picture: Where Did the Chain Break?

When a PC will not start, the most useful question is: how far did it get? The boot chain (Section 10) has a fixed order. Whatever you saw last tells you which link broke.

A simple, safe routine for any failure:

1. Write down the exact message, code or last thing you saw.
2. Change one thing at a time.
3. Do not reinstall Windows until you have tried the repairs below. Your files may be safe and recoverable.
4. Back up what you can before risky repairs (for example, copy files with a recovery USB stick).

11.1 Black Screen (Before POST)

What it is: The PC shows no sign of life, or shows life (fans) with a black screen and no POST. The problem is in Section 2: power, the CPU, RAM, or the display connection.

Case A: nothing happens, no lights, no fans.

Case B: fans spin, but nothing on the screen.

Laptops: Unplug the charger, hold the power button for 30 seconds to drain it, and try again. Also check that a charger with the right power rating is used.

11.2 POST Failures (Beep Codes)

What it is: The screen is black, but the board speaks: beeps, lights or a code. Section 3.5 listed the types. Here is how to act on them.

The method:

1. Hear or see the pattern and write it down. (Count short and long beeps exactly.)
2. Find your board model (msinfo32 if it still runs on another PC, or read the board itself) and open its manual. Beep codes differ by maker.
3. Fix the part it names.

Common causes and cures:

Messages on the screen (when you can see them):

Rule: If the PC worked before, ask: what changed? New RAM, a new card, a firmware update, or a changed setting is the usual culprit. Undo it first.

11.3 No Bootloader Found

What it is: POST finished fine, but the firmware (or the Windows boot manager) cannot find or run the next program in the chain. You see text on a plain screen such as "No bootable device", "Reboot and Select proper Boot device", "Operating System not found", "Boot Configuration Data file is missing" or "Windows failed to start".

Here is a real example of the last kind:

Figure 6.9 — A "Windows failed to start" screen. It names the file \Windows\system32\winload.exe, the status 0xc000000f, and the information line says the selected entry could not be loaded because the application is missing or corrupt. It also lists repair steps. This is the boot manager telling you it could not run the loader. Screenshot: EnigmaLord515, CC BY-SA 4.0, via Wikimedia Commons.

Common causes:

The first checks (all safe):

1. Unplug USB drives and other disks, then restart.
2. Enter firmware setup and check the disk is listed. If it is not, check the cable (SATA) or reseat the SSD (M.2). If it is still missing, the disk or its connection has failed.
3. Check the boot order and the boot mode (UEFI vs Legacy). Windows installed in UEFI mode will not boot in Legacy mode.

The Windows Recovery Environment (WinRE). WinRE is a small repair version of Windows. You can reach it by:

• Letting Windows fail to boot two or three times. It then starts Automatic Repair itself.
• Booting from a Windows installation USB and choosing Repair your computer.
• Pressing Shift + Restart when you can still sign in.

In WinRE, choose Troubleshoot → Advanced options. The tools there:

Manual repair from the WinRE Command Prompt.

Rebuild boot files with bootrec (it works mostly on BIOS/MBR layouts):

bootrec /scanos
bootrec /rebuildbcd
bootrec /fixmbr
bootrec /fixboot

On a UEFI/GPT PC, the usual cure is to recreate the boot files from your Windows folder with bcdboot. The steps (WinRE Command Prompt):

1. Start diskpart, then list disk, select disk 0, list vol.
2. Find the small FAT32 volume of about 100 MB or more (the ESP). Select it with select vol N, then give it a letter: assign letter=S. Then exit.
3. Run (assuming Windows is on C:; in WinRE, the letter can differ, so check with dir):

bcdboot C:\Windows /s S: /f UEFI

This copies fresh boot files to the ESP and makes a new boot entry. Read each step carefully. Choosing the wrong disk in diskpart can erase data. If you are not sure, stop and ask for help.

If the file system is damaged, check it from the same Command Prompt:

chkdsk C: /f

11.4 Kernel Crash (BSOD During Boot)

What it is: The loader works, the Windows logo shows, then the screen turns blue with a sad face and a stop code. This is a BSOD (Blue Screen of Death), the kernel's way of stopping when it finds something it cannot safely continue past. The stop code names the problem.

Stop codes that happen during boot:

The screen may also show a QR code and a file name (like somedriver.sys). Write down the code and the file.

What to do:

1. Stop an automatic restart loop so you can read the code. In WinRE → Startup Settings, choose Disable automatic restart after failure.
2. Think about what changed: a new driver, update, hardware or firmware setting. Undo it. (In WinRE: Uninstall Updates or System Restore.)
3. Test memory with mdsched.exe (Windows Memory Diagnostic) or by removing a RAM stick.
4. Check the disk: chkdsk C: /f, and the disk's health (see the maker's tool, or Get-PhysicalDisk in PowerShell once you are in Windows).
5. Repair system files from the WinRE Command Prompt:

sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
DISM /Image:C:\ /Cleanup-Image /RestoreHealth

(sfc is System File Checker. DISM is the Deployment Image Servicing and Management tool. In WinRE the drive letters can differ, so confirm the Windows drive first. DISM with /RestoreHealth may need a source or an internet connection.)

6. If it works in Safe Mode, the fault is a driver or a startup program (Section 11.5).

Reading the dump after you are back in Windows. The kernel saves a dump file when it crashes: small ones in C:\Windows\Minidump and a bigger one named C:\Windows\MEMORY.DMP. Event Viewer's System log also records the crash: Event ID 41 (Kernel-Power) means the PC restarted without a clean shutdown, and Event ID 1001 (BugCheck) shows the stop code. Free tools such as WinDbg or BlueScreenView can read the dumps. (They are not part of Windows; download only from the official sites.)

11.5 Driver Failure

What it is: A driver (Section 6.2 and 7.4) fails to load or crashes. Because drivers run with the kernel's full power, a bad driver can crash the whole system. The signs differ depending on which driver.

How to find the guilty driver:

1. Boot into Safe Mode: from WinRE, Troubleshoot → Advanced options → Startup Settings → Restart → 4 (Safe Mode). Only core drivers load, so a PC that fails normally may work.
2. Boot logging. Choose Enable boot logging in Startup Settings. Windows writes every driver it loads to C:\Windows\ntbtlog.txt. The last driver in the list (or one marked "Did not load") is a clue.
3. Open Event Viewer → Windows Logs → System and look for errors (red) near the time of the failure. Event ID 7026 says a boot-start or system-start driver failed to load, and Event ID 7000/7001 relate to services.
4. In Device Manager, look for yellow triangles. Right-click → Properties shows an error code (for example Code 31 or Code 43) and a message.

How to fix:

Common culprits: Newly installed graphics, antivirus, VPN, storage (RAID) and virtual machine drivers. Think about what you installed just before the trouble began.

11.6 Services Failure Preventing Login

What it is: The kernel and drivers are fine, the system has reached user mode, but a service or a sign-in component fails, so you get stuck: a blank or blue screen after the logo, no sign-in box, an endless "Please wait...", or a message such as "The User Profile Service failed the sign-in".

How to approach it:

1. Try Safe Mode (11.5). Services that are not core do not start, so you can sign in and look around.
2. Read the logs. In Event Viewer → System, look for Service Control Manager errors: 7000, 7001 (a service or its dependency failed), 7009 (a service timed out) and 7034 (a service stopped unexpectedly). Under Application, look for crashes of explorer.exe.
3. Use another administrator account to sign in, if there is one. If a new account works, your profile is the problem, not Windows.
4. Repair system files with sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth (from Safe Mode, in an administrator Command Prompt).
5. Use System Restore to return to a time when sign-in worked.
6. If you sign in but see only a black screen, press Ctrl + Alt + Del, choose Task Manager, then File → Run new task. For example, run explorer.exe to see whether the desktop starts, or services.msc to look at services.
7. Back up your files before more drastic steps: boot a recovery USB and copy your C:\Users\YourName folder to an external disk.

Last resort: Reset this PC (Settings → System → Recovery). It can keep your files and reinstall Windows. A fresh installation is the final step, after backing up.

Where it stopped  ─►  Where to look
Before logo       ─►  Power, RAM, CPU, firmware settings, boot order
Logo, then BSOD   ─►  Stop code, drivers, disk, memory
Logo, endless dots─►  Safe Mode, ntbtlog.txt, recent updates
No sign-in screen ─►  Safe Mode, Event Viewer (System log), sfc/DISM
Black screen      ─►  Task Manager → Run new task → explorer.exe, profile

Summary