Hi Cliffton,

The most common reasons for BOOTMGR errors include corrupt and misconfigured files, hard drive and operating system upgrade issues, corrupt hard drive sectors, and outdated BIOS.

Please try below fixes to resolve the issue.

Solution 1: Restart Your Desktop or Laptop

Once Windows prompts you BOOTMGR is missing, please try to restart your PC by pressing Ctrl+Alt+Del keys or any key, just do as the error message suggests since maybe BOOTMGR error is a fluke. However, to a great extent, only a rebooting can’t repair BOOTMGR. So please try the next way.

Solution 2: Remove All Removable Media

Since BOOTMGR error can be caused by booting your computer from a non-bootable hard drive. So you should check whether your PC is configured to boot from a USB flash drive, a floppy disk, or other unbootable disks. If it is, please remove it and make sure your BIOS doesn’t load from any of them. Otherwise, missing BOOTMGR issue will happen again.

Solution 3: Change Boot Order in BIOS

After unplugging a non-bootable disk, perhaps BOOTMGR error still appears. In this case, you need to consider checking the boot sequence in BIOS.

1. Restart your computer.
2. Then press a specific key to go to the main interface of BIOS.
Note: The key is different depending on different computers and different Windows operating systems. It will be either F2 or F12.

3. Then under "Boot" tab, modify the boot order so that the hard drive is set as the first boot device.



After restarting the PC, if the issue also happens, just try the next way. 

Solution 4: Perform Windows Startup Repair

In addition, you also can perform a Windows startup repair. This way can replace any missing or corrupted files, including BOOTMGR. You may ask: If there is no CD disc, can BOOTMGR is missing Windows 7 fix without CD be done? Of course, in Windows 7, you can press F8 to go to startup option.



Solution 5: Perform a Clean Windows Installation

If all solutions can’t work to solve Boot Manager missing issue, it is a good way to perform a Windows installation for this error repair. This way will completely remove Windows from your PC. However, all data will be deleted. So you had better back up important files before reinstalling OS. 

I hope this helps.

Regards,
Lokesh