Start your PC and use the F11 to boot into recovery mode.
Next select Advanced and then Command prompt.
Please follow these steps to boot into Recovery Environment and try to rebuild BCD.
a. Boot into Windows Recovery Environment using the Windows 10 USB or DVD.
b. Click on Repair your computer.
c. Click on Troubleshoot and in theAdvanced options.
d. Select Command Prompt. Type the following commands into the prompt and press Enter key after each command.
From here run chkdsk c: /r /x and watch the magic work. If
chkdsk only scans you will need to run sfc /scannow and reboot.