You need to use a repair disc or a recovery drive that was created on a working Windows computer. However, because you already have startup issues, it's obvious that you won't be able to simply run it from Windows. In order to be able to use Bootrec.exe, you'll have to use Command Prompt. How to start the Command Prompt when Windows won't load successfully The Boot Configuration Data is stored in a data file that has the same format as the Windows Registry.

Boot Configuration Data (BCD) - The BCD is a database of boot-time configuration data that is used by the Windows Boot Manager.

In Windows 7 and newever versions of Windows, the boot sector loads the Windows Boot Manager, accesses the Boot Configuration Data and uses this information to load the operating system If this signature is corrupted, or has been changed, the BIOS will not be able to find the boot sector and won't be able to load the necessary instructions for finding and starting the operating system. A boot sector must have a specific disk signature to be seen by BIOS as a boot sector.

Boot sector - the region of the disk that contains the code to be loaded into the RAM memory, that is necessary to load the operating system.

Its purpose is to tell the computer's BIOS where to look for the operating system, so that it can start it.

Master Boot Record (MBR) - the first sector of your system drive.

If you need to know what all these mean, here's an explanation for each of them: With this tool you can repair the Master Boot Record (MBR), write a new boot sector, rebuild the Boot Configuration Data (BCD) and add missing Windows installations to the boot configuration data. No matter whether you use Windows 7 or Windows 10, if your operating system has trouble booting and Startup Repair can't fix the problem, it's worth trying the Bootrec.exe tool.

Bootrec.exe - The ultimate repair tool for boot problems in Windows NOTE: This guide covers Windows 10, Windows 7 and Windows 8.1.

Bootrec /fixboot windows 10