Explanation The error "BOOTMGR is missing" indicates that the boot sector is damaged or missing1. The boot sector is a part of the hard disk that contains the code and information needed to start Windows1. To fix this error, one of the possible methods is to run Startup Repair from Windows Recovery Environment (WinRE)1. Startup Repair is a tool that can automatically diagnose and repair problems with the boot process2. References: 1: "Bootmgr is missing Press Ctrl+Alt+Del to restart" error when you start Windows (https://support.microsoft.com/en-us/topic/-bootmgr-is-missing-press-ctrl-alt-del-to-restart-error-when-you-start- 2: Startup Repair: frequently asked questions (https://support.microsoft.com/en-us/windows/startup-repair-frequently-asked-questions-f5f412a0-19c4-8e0a-9f6