Run sfc/scannow on external hardrive to restore windows settings

My laptop recently died and it turned out the hardrive had come lose. I plugged it back in but now when it tries to boot up it keeps trying to do a system repair. The system repair keeps reporting that it cant find any faults, but wont fully load windows. I think I need to repair the windows files on the drive.

To try and rectify this, Ive took the laptop hardrive out, plugged it into my PC, and run chkdsk on it which found some faults and said it resolved them. Id now like to run sfc /scannow on the drive.

Im using this in the command line 'sfc /scannow /offbootdir=d:\ /offwindir=d:\windows' where d is the external drive but it comes up saying "Windows Resource Protection could not perform the requested operation"

Any ideas how to get by this?

Thanks.

Its the command prompt you get when startup repair runs. When i try and run SFC, its now telling me a repair is in progress and i need to reboot. Doing so just boots back to the repair and i cant get any further.

Regarding the drive letter, when the startup repair runs, its says there is a CORRUPTBOOTMASTER. The main windows file are on drive D although after working through some of the threads in this forum, the drive letter has changed from D, to C and now back to D again. Guess its because of been using DISKPART (not sure ive been using it correctly) and also tried to fix the boot records.