Sorry, you are correct about the last part. But yes that's what I'm saying. Your pc will run with your friends HDD in it, it'll just complain at start up. But if the boot partition is fucked it's not going to matter.
Probably just a boot corruption. You could have installed that drive in your pc as the only drive. Windows would have complained but then setup devices and booted as normal (assuming no other issues.) That way your not risking your own files.
I just had Linux mint do something very similar. After a reinstall everything is working normal.
Got it so never buying this game. Maybe I'll pirate it for my wife now.