I also had a boot loop problem after an attempted windows 10 update.
Tried a few things myself like creating a windows 10 usb installation disk to boot from.
Was able to get to the troubleshooting screen but the startup repair, system restore didn't work. Did get the command prompt to work so I could copy off important files.
I contacted MS support and they pointed me to this article which solved my problem.
Even though it mentions windows 7 and Vista, the same commands work for Win 10.