Repairing Boot Errors in Windows 10

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If your computer doesn't start, it's easy to panic. Fortunately, if your boot problem is related to the Master Boot Record (MBR), as in the case of "Windows failed to start" messages, it is not too difficult to solve.

The MBR is a hard disk region on your computer that contains information about the hard disk partitions. It also contains information on how the computer should load the operating system. While MBR is an older scheme that expires in favor of GPT (GUID Partition Table), many computers still use MBR for backwards compatibility.

Solution 1 - Booting from a Device

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If you cannot repair your PC, you must boot it from a recovery CD or DVD or a new copy of Windows 10.

Congratulations if you did a collection before you needed it, it was too late to do one at the time.

If not, you can repair or reinstall Windows 10 from an 8GB DVD or USB stick. Microsoft provides the code and instructions online. You don't need to worry about a product key because your PC authenticates online and your activation information is stored against the email address of the Microsoft account you use to log in to Windows 10. However, you must take care of the start order.

Solution 2 - Repair MBR Master Boot Record

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The process is almost identical for Windows 10/8/7. First, you need a Windows installation DVD. Without it, it's gonna be hard to move on.

Step 1: Press F8 during system boot to access the Windows recovery menu. Unlike other versions, the Windows 8 recovery menu has the Metro UI style.

Step 2: Click Troubleshooting.

Step 3: Click Advanced Options to access the Auto Repair menu.

Step 4: We need the Bootrec.exe tool. Click the command prompt and type the following commands in order:

bootrec /RebuildBcd
bootrec /fixMbr
bootrec /fixboot /fixboot

Exit the program and restart your system. In some cases, you may need to execute additional commands.

bootsect /nt60 SYS or bootsect /nt60 ALL

Solution 3 - Add missing Windows installations to boot configuration data.

boot-configuration-data

If you have several operating systems installed on your computer, but not all of them are available, use the /ScanOS option. If you use this setting on Bootrec.exe, a scan is run on all hard disks for all Windows installations that are not currently included in the boot configuration data (BCD).

If the command bootrec.exe /scanos returns the results, you can continue the repair process. At the end, you recover the lost Windows installation in the secure BCD table and you can restart.

You must first clean the Master Boot Record (MBR) with bootrec /fixmbr. Then type bootsect.exe /nt60 all /force and press Enter. The /nt60 parameter applies the BOOTMGR compatible master boot code. The /all argument updates the master boot code on all partitions. The parameter /force forcibly removes the volume(s) during the boot code update so that the Bootsect.exe tool does not have exclusive access to the volume.

Running all these commands creates a new MBR and asks it to use the correct Windows boot loader to load that particular installation from your disk.

Here is an overview of how to repair a defective Windows 10 installation. Although these events should be extremely rare for most everyday users, they can occur during more risky operations, such as reinstalling Windows, resizing partitions, or configuring a dual boot. Although the above steps may help, it is always a good idea to make a full backup in advance.

https://www.theguardian.com/technology/askjack/2017/apr/20/windows-10-fix-pc-laptop-will-not-boot