You can use either if you can get the machine to boot up with them.
You can also try bootrec /fixboot
That may run better in Win 8.1 than it does in Win 10 1709.
If the bootrec cmds don't do anything, boot back up with the install media and go back to the Command Prompt and enter -
bcdedit |find "osdevice"
and using that partition letter instead of the x I have exampled, enter chkdsk x: /r to see what that reports.
For clarity, that's a Pipe symbol before find in the bcdedit cmd and is the uppercase of \
Enter exit to close the cmd window, remove the install media and shutdown then see what it's like on the reboot.
If that's still a no go then boot back up with the install media back to the cmd prompt and enter this cmd, again using your partition letter instead of the X I have exampled.
sfc /scannow /offbootdir=X:\ /offwindir=X:\Windows and see what that reports.
Note the space before each /