If you haven’t shut down Windows 8/10 properly, it may cause corrupted system files and result in the error message below when you power on your computer.
Your PC/Device needs to be repaired
The Boot Configuration Data for your PC is missing or contains errors.

To fix this error, you can use ‘Startup Repair’ which is an option in Advanced Startup. So you need Windows installation media or recovery drive and follow steps below.
1. Insert Windows installation disc or connect recovery drive and boot to Advanced Startup.
2. On Windows Setup, click ‘Next’.
3. Select ‘Repair your computer’.
4. On Choose an option, select ‘Troubleshoot’.
5. Select ‘Advanced options’ and select ‘Startup Repair’.
6. When finishes, remove the installation media or recovery drive. If succeed, your computer should boots into Windows normally.

* If this method can’t fix your problem, you can check other methods at the link below.

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Resources
Windows error message /”Bootmgr is missing Press Ctrl+Alt+Del to restart/”
https://support.microsoft.com/en-us/kb/2622803

Create Bootable USB Flash Drive from ISO image with Rufus
https://www.youtube.com/watch?v=Bk2scAn9vyo

Download Windows 8.1 installation media
https://www.microsoft.com/en-us/software-download/windows8

Download Windows 10 installation media
https://www.microsoft.com/en-us/software-download/windows10

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