What stage of upgrade are you on? Have you had win 10 for a while and its only started doing this? Or were you upgrading it now?
is there anything on C drive you want to rescue? try making this on another PC: http
/www.howtogeek.com/howto/windows-vista/use-ubuntu-live-cd-to-backup-files-from-your-dead-windows-computer/
Also, on another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB
you can try start up repair if PC had win 10 on it for a while
change boot order so USB is first, hdd second
boot from installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose advanced
choose start up repair - this will scan PC and maybe fix this - will ask for logon info