Was it at startup as most updates run when you shut PC down or at startup? Only certain updates take longer, they are version updates and can take 40 minutes or so... is that what it was doing???
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 - just a boot disk
Lets try to get to safe mode
change boot order so USB is first, hdd second
boot from installer, on 2nd screen after languages, choose repair this pc, not install
choose troubleshoot
choose advanced
choose start up options
hit the restart button
choose a safe mode (it doesn't matter which) by using number associated with it.
PC will restart and load safe mode
just restarting after getting into safe mode might be enough
If you restarted during a long update you might be best clean installing as no way to know what it was doing. long updates are version updates, its essentially a new copy of windows 10