Windows 10 bootrec /fixboot access is denied
Windows 10 Installation Media:
Insert the Media (DVD/USB) in your PC and restart.
Boot from the media.
Select Repair Your Computer.
Select Troubleshoot.
Choose Command Prompt from the menu
Diskpart
List disk (Note which disk is your Boot drive number mine is 0)
Sel disk 0
List vol (Note which volume is the EFI partition mine is 4)
Sel vol 4
assign letter=V:
Exit
V:
possible format V: /FS:FAT32
bcdboot C:\windows /s V: /f UEFI
or
bcdboot C:\windows /s V: /f ALL
other commands
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd - this tends to fail so have tol do the above