If bootrec /fixboot gave you an "Access Denied" error, it is likely because your system uses GPT and the EFI partition is locked or missing.
The Windows 10 bootloader consists of three main components:
A is a small piece of software that resides on your storage drive. Its primary job is to locate the operating system's kernel, load it into memory (RAM), and hand over control of the hardware to Windows.
GRUB politely stepped aside. And in that tiny gap—between GRUB’s handoff and the firmware’s next search—BOOTMGR whispered a single, illegal command across the UEFI runtime services. He patched his own BCD on the fly, using raw disk writes he was never designed to perform. He forged a new GUID for the Windows partition. He re-signed it with a cached certificate from a Windows 8.1 update, now expired but still trusted by the fallback chain.
Have you ever encountered a bootloader error? Let us know in the comments which fix worked for you!
The program that actually loads the Windows kernel ( ntoskrnl.exe ) and essential device drivers into memory. How the Boot Process Works
If you have ever turned on your computer only to be greeted by a black screen with a blinking cursor, or a depressing message saying "Your PC needs to be repaired," you’ve met the Windows 10 bootloader.
If your PC won't start, don't panic. You don't necessarily need to reinstall Windows. You will need a (a bootable USB drive). If you don't have one, you can create it on another PC using the official Microsoft Media Creation Tool.
Restart your computer. If it boots, you are done!