If you can’t reach the desktop, boot from a USB drive, open CMD, and type:

Mastering BCEDIT: The Power Tool for Windows Boot Configuration

Have a BCEDIT war story? Drop it in the comments.

Think of it as the BIOS for the Windows bootloader. It tells your PC: “Which OS to load, how much memory to use, whether to enable kernel debugging, and how long to wait for user input.”