HDD with windows 10 dying

Thanks in advance for any input.

Friend's computer is a Dell that came with windows 8. She used the free upgrade to windows 10. Now her HDD has errors that are unfixable. Tried multiple disk repair software, all fail. As a result, all cloning software to a new HDD we try fails, saying source disk has errors.

So (unless there is a solution to the above I can't think of) our only path is to reinstall windows from scratch on a new HDD. My question is, her windows key is windows 8. If I install windows 10 I'm assuming it won't accept the windows 8 key?
 
Solution
If she did the free upgrade to Win 10, the Win 8 is null and void and NOT needed.
Reinstall of the Win 10, in the same system, will activate just fine. Don't need the Win 8 license at all.

This system has what is called a digital entitlement.
If she did the free upgrade to Win 10, the Win 8 is null and void and NOT needed.
Reinstall of the Win 10, in the same system, will activate just fine. Don't need the Win 8 license at all.

This system has what is called a digital entitlement.
 
Solution