The good news is that you don't need to download Bootmgr separately. Bootmgr is an integral part of Windows 7, and you can repair or restore it using built-in tools. Here are the methods:
(If you are using a Windows 7 USB drive, the path may be something like E:\bootmgr .)
On the "Install Now" screen, click Repair your computer in the bottom-left corner. windows 7 bootmgr download
If none of the above works, use System Restore (if available) to revert to a previous working state. From the System Recovery Options dialog, select and follow the prompts. If System Restore fails, a clean installation of Windows 7 (preserving your data by choosing Upgrade or using an installation repair) may be necessary.
Your computer is trying to boot from a non-bootable device, like a USB flash drive or external hard drive left plugged in. The good news is that you don't need
The file became unreadable due to a system crash or sudden power loss.
If your PC came with Windows 7 preinstalled, the manufacturer (Dell, HP, Lenovo, etc.) typically provides a recovery partition or recovery discs that can repair boot issues. If none of the above works, use System
BOOTMGR (Windows Boot Manager) is a component of the Windows operating system that is responsible for loading the operating system. It's a critical part of the boot process, and issues with BOOTMGR can prevent Windows from booting properly.