Flip 15 will not boot - Error code: 0xc000000f

I downgraded from Windows 10 to 8.1 the other day and after rebooting I got the error message below.

'Recovery

Your PC needs to be repaired

The boot configuration date for your PC is missing or contains errors

File \EFI\Microsoft\Boot\BCD

Error code: 0xc000000f

I have tried 8.1 installation media via USB as my Vaio doesn't have an optical drive and each time I got in to it I get that blue screen and when I press refresh or re-install it says "The drive where Windows is installed is locked.Unlock the drive and try again."

What can I do to resolve this? I have tried check disk, tried bootrec but nothing works, any help would be gratefully appreciated.

(If the hard drive needs replacing, what would I need and where do I get it from?)