careful you messed up once doing that .... do not try to boot from another System or HDD, If you DL an Win10XPE, burn to a USB then use that to boot to your (messed up) computer you should be able to copy/paste all you want from the old HDD, to a different place and save it,
then insert an proper USB with new Windows 10 ISO and do a clean install, therefore fixing your computer....