Fixing Windows boot problems with BootSec.exe and BootRec.exe

Sometimes, developer life requires some PC resurrection. If your Windows fails to start, the Master Boot Record (MBR) or boot configuration may be corrupted. You can fix these from Recovery Environment using Bootrec or Bootsect commands.

Here's how:

1) Boot from Windows installation media - "Repair your computer" - "Troubleshoot" - "Command Prompt".

2) Rebuild the boot sector:

bootsect /nt60 SYS

The above command rewrites the boot sector on the system partition to use the Windows 7/8/10 boot loader.

3) Use Bootrec to repair MBR and rebuild the BCD store:

bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd

If the "/fixboot" option reports "Access is denied", then you need to assign a drive letter to the EFI partition first using DiskPart, then retry.

Finally, exit and reboot:

exit
wpeutil reboot

These tools only modify boot records, so your user data stays intact.