Advanced troubleshooting for Windows boot problems

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This article is intended for use by support agents and IT professionals. If you're looking for more general information about recovery options, see Recovery options in Windows 10.

Applies to:   Windows 10


There are several reasons why a Windows-based computer may have problems during startup. To troubleshoot boot problems, first determine in which of the following phases the computer gets stuck:

Phase Boot Process BIOS UEFI
1 PreBoot MBR/PBR (Bootstrap Code) UEFI Firmware
2 Windows Boot Manager %SystemDrive%\bootmgr \EFI\Microsoft\Boot\bootmgfw.efi
3 Windows OS Loader %SystemRoot%\system32\winload.exe %SystemRoot%\system32\winload.efi
4 Windows NT OS Kernel %SystemRoot%\system32\ntoskrnl.exe
  1. PreBoot: The PC's firmware initiates a power-on self test (POST) and loads firmware settings. This pre-boot process ends when a valid system disk is detected. Firmware reads the master boot record (MBR), and then starts Windows Boot Manager.

  2. Windows Boot Manager: Windows Boot Manager finds and starts the Windows loader (Winload.exe) on the Windows boot partition.

  3. Windows operating system loader: Essential drivers required to start the Windows kernel are loaded and the kernel starts to run.

  4. Windows NT OS Kernel: The kernel loads into memory the system registry hive and other drivers that are marked as BOOT_START.

    The kernel passes control to the session manager process (Smss.exe) which initializes the system session, and loads and starts the devices and drivers that aren't marked BOOT_START.

Here's a summary of the boot sequence, what will be seen on the display, and typical boot problems at that point in the sequence. Before you start troubleshooting, you have to understand the outline of the boot process and display status to ensure that the issue is properly identified at the beginning of the engagement. Select the thumbnail to view it larger.

Diagram of the boot sequence flowchart.

Each phase has a different approach to troubleshooting. This article provides troubleshooting techniques for problems that occur during the first three phases.


If the computer repeatedly boots to the recovery options, run the following command at a command prompt to break the cycle:

Bcdedit /set {default} recoveryenabled no

If the F8 options don't work, run the following command:

Bcdedit /set {default} bootmenupolicy legacy

BIOS phase

To determine whether the system has passed the BIOS phase, follow these steps:

  1. If there are any external peripherals connected to the computer, disconnect them.

  2. Check whether the hard disk drive light on the physical computer is working. If it's not working, this dysfunction indicates that the startup process is stuck at the BIOS phase.

  3. Press the NumLock key to see whether the indicator light toggles on and off. If it doesn't toggle, this dysfunction indicates that the startup process is stuck at BIOS.

    If the system is stuck at the BIOS phase, there may be a hardware problem.

Boot loader phase

If the screen is black except for a blinking cursor, or if you receive one of the following error codes, this status indicates that the boot process is stuck in the Boot Loader phase:

  • Boot Configuration Data (BCD) missing or corrupted
  • Boot file or MBR corrupted
  • Operating system Missing
  • Boot sector missing or corrupted
  • Bootmgr missing or corrupted
  • Unable to boot due to system hive missing or corrupted

To troubleshoot this problem, use Windows installation media to start the computer, press Shift+F10 for a command prompt, and then use any of the following methods.

Method 1: Startup repair tool

The Startup Repair tool automatically fixes many common problems. The tool also lets you quickly diagnose and repair more complex startup problems. When the computer detects a startup problem, the computer starts the Startup Repair tool. When the tool starts, it performs diagnostics. These diagnostics include analyzing startup log files to determine the cause of the problem. When the Startup Repair tool determines the cause, the tool tries to fix the problem automatically.

To do this task of invoking the Startup Repair tool, follow these steps.


For additional methods to start WinRE, see Windows Recovery Environment (Windows RE).

  1. Start the system to the installation media for the installed version of Windows. For more information, see Create installation media for Windows.
  2. On the Install Windows screen, select Next > Repair your computer.
  3. On the Choose an option screen, select Troubleshoot.
  4. On the Advanced options screen, select Startup Repair.
  5. After Startup Repair, select Shutdown, then turn on your PC to see if Windows can boot properly.

The Startup Repair tool generates a log file to help you understand the startup problems and the repairs that were made. You can find the log file in the following location:


For more information, see Troubleshoot blue screen errors.

Method 2: Repair boot codes

To repair boot codes, run the following command:


To repair the boot sector, run the following command:



Running BOOTREC together with Fixmbr overwrites only the master boot code. If the corruption in the MBR affects the partition table, running Fixmbr may not fix the problem.

Method 3: Fix BCD errors

If you receive BCD-related errors, follow these steps:

  1. Scan for all the systems that are installed. To do this step, run the following command:

    Bootrec /ScanOS
  2. Restart the computer to check whether the problem is fixed.

  3. If the problem isn't fixed, run the following commands:

    bcdedit /export c:\bcdbackup
    attrib c:\boot\bcd -r -s -h
    ren c:\boot\bcd bcd.old
    bootrec /rebuildbcd
  4. Restart the system.

Method 4: Replace Bootmgr

If methods 1, 2 and 3 don't fix the problem, replace the Bootmgr file from drive C to the System Reserved partition. To do this replacement, follow these steps:

  1. At a command prompt, change the directory to the System Reserved partition.

  2. Run the attrib command to unhide the file:

    attrib -r -s -h
  3. Navigate to the system drive and run the same command:

    attrib -r -s -h
  4. Rename the bootmgr file as bootmgr.old:

    ren c:\bootmgr bootmgr.old
  5. Navigate to the system drive.

  6. Copy the bootmgr file, and then paste it to the System Reserved partition.

  7. Restart the computer.

Method 5: Restore system hive

If Windows can't load the system registry hive into memory, you must restore the system hive. To do this step, use the Windows Recovery Environment or use the Emergency Repair Disk (ERD) to copy the files from the C:\Windows\System32\config\RegBack directory to C:\Windows\System32\config.

If the problem persists, you may want to restore the system state backup to an alternative location, and then retrieve the registry hives to be replaced.


Starting in Windows 10, version 1803, Windows no longer automatically backs up the system registry to the RegBack folder.This change is by design, and is intended to help reduce the overall disk footprint size of Windows. To recover a system with a corrupt registry hive, Microsoft recommends that you use a system restore point. For more information, see The system registry is no longer backed up to the RegBack folder starting in Windows 10 version 1803.

Kernel phase

If the system gets stuck during the kernel phase, you experience multiple symptoms or receive multiple error messages. These error messages include, but aren't limited to, the following examples:

To troubleshoot these problems, try the following recovery boot options one at a time.

Scenario 1: Try to start the computer in Safe mode or Last Known Good Configuration

On the Advanced Boot Options screen, try to start the computer in Safe Mode or Safe Mode with Networking. If either of these options works, use Event Viewer to help identify and diagnose the cause of the boot problem. To view events that are recorded in the event logs, follow these steps:

  1. Use one of the following methods to open Event Viewer:

    • Go to the Start menu, select Administrative Tools, and then select Event Viewer.
    • Start the Event Viewer snap-in in Microsoft Management Console (MMC).
  2. In the console tree, expand Event Viewer, and then select the log that you want to view. For example, choose System log or Application log.

  3. In the details pane, open the event that you want to view.

  4. On the Edit menu, select Copy. Open a new document in the program in which you want to paste the event. For example, Microsoft Word. Then select Paste.

  5. Use the up arrow or down arrow key to view the description of the previous or next event.

Clean boot

To troubleshoot problems that affect services, do a clean boot by using System Configuration (msconfig). Select Selective startup to test the services one at a time to determine which one is causing the problem. If you can't find the cause, try including system services. However, in most cases, the problematic service is third-party.

Disable any service that you find to be faulty, and try to start the computer again by selecting Normal startup.

For detailed instructions, see How to perform a clean boot in Windows.

If the computer starts in Disable Driver Signature mode, start the computer in Disable Driver Signature Enforcement mode, and then follow the steps that are documented in the following article to determine which drivers or files require driver signature enforcement: Troubleshooting boot problem caused by missing driver signature (x64)


If the computer is a domain controller, try Directory Services Restore mode (DSRM).

This method is an important step if you encounter Stop error "0xC00002E1" or "0xC00002E2"



Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft can't guarantee that these problems can be solved. Modify the registry at your own risk.


To troubleshoot this Stop error, follow these steps to filter the drivers:

  1. Go to Windows Recovery Environment (WinRE) by putting an ISO disk of the system in the disk drive. The ISO should be of the same version of Windows or a later version.

  2. Open the registry.

  3. Load the system hive, and name it test.

  4. Under the following registry subkey, check for lower filter and upper filter items for non-Microsoft drivers:


  5. For each third-party driver that you locate, select the upper or lower filter, and then delete the value data.

  6. Search through the whole registry for similar items. Process as appropriate, and then unload the registry hive.

  7. Restart the server in Normal mode.

For more troubleshooting steps, see Advanced troubleshooting for Stop error 7B or Inaccessible_Boot_Device.

To fix problems that occur after you install Windows updates, check for pending updates by using these steps:

  1. Open a Command Prompt window in WinRE.

  2. Run the command:

    DISM /image:C:\ /get-packages
  3. If there are any pending updates, uninstall them by running the following commands:

    DISM /image:C:\ /remove-package /packagename: name of the package
    DISM /Image:C:\ /Cleanup-Image /RevertPendingActions

    Try to start the computer.

If the computer doesn't start, follow these steps:

  1. Open a command prompt window in WinRE, and start a text editor, such as Notepad.

  2. Navigate to the system drive, and search for windows\winsxs\pending.xml.

  3. If the pending.xml file is found, rename the file as pending.xml.old.

  4. Open the registry, and then load the component hive in HKEY_LOCAL_MACHINE as test.

  5. Highlight the loaded test hive, and then search for the pendingxmlidentifier value.

  6. If the pendingxmlidentifier value exists, delete it.

  7. Unload the test hive.

  8. Load the system hive, name it test.

  9. Navigate to the following subkey:


  10. Change the Start value from 1 to 4.

  11. Unload the hive.

  12. Try to start the computer.

If the Stop error occurs late in the startup process, or if the Stop error is still being generated, you can capture a memory dump. A good memory dump can help determine the root cause of the Stop error. For more information, see Generate a kernel or complete crash dump.

For more information about page file problems in Windows 10 or Windows Server 2016, see Introduction to page files.

For more information about Stop errors, see Advanced troubleshooting for Stop error or blue screen error issue.

Sometimes the dump file shows an error that's related to a driver. For example, windows\system32\drivers\stcvsm.sys is missing or corrupted. In this instance, follow these guidelines:

  • Check the functionality that's provided by the driver. If the driver is a third-party boot driver, make sure that you understand what it does.

  • If the driver isn't important and has no dependencies, load the system hive, and then disable the driver.

  • If the stop error indicates system file corruption, run the system file checker in offline mode.

    • To do this action, open WinRE, open a command prompt, and then run the following command:

      SFC /Scannow /OffBootDir=C:\ /OffWinDir=C:\Windows

      For more information, see Using system file checker (SFC) to fix issues.

    • If there's disk corruption, run the check disk command:

      chkdsk /f /r
  • If the Stop error indicates general registry corruption, or if you believe that new drivers or services were installed, follow these steps:

    1. Start WinRE, and open a command prompt window.
    2. Start a text editor, such as Notepad.
    3. Navigate to C:\Windows\System32\Config\.
    4. Rename the all five hives by appending .old to the name.
    5. Copy all the hives from the Regback folder, paste them in the Config folder, and then try to start the computer in Normal mode.


Starting in Windows 10, version 1803, Windows no longer automatically backs up the system registry to the RegBack folder.This change is by design, and is intended to help reduce the overall disk footprint size of Windows. To recover a system with a corrupt registry hive, Microsoft recommends that you use a system restore point. For more information, see The system registry is no longer backed up to the RegBack folder starting in Windows 10 version 1803.