With Windows 10, unfortunately Microsoft did away with many methods that us technicians would use to repair a corrupted or otherwise non-booting Windows computer. Instead, Microsoft has come up with the idea of a "Recovery Drive" which is a USB drive that the user has to make that contains critical information about their computer and can be used to boot and repair Windows 10 should something go wrong. Unfortuantely this is not anything that is done automatically and Microsoft isn't good about getting the message out to users. All Windows 10 users should be sure to create a Windows 10 Recovery Drive and keep it on hand in the event something goes wrong with their computer and renders it unbootable. All that's needed is a USB flash drive of at least 8GB (larger might be necessary in some instances). Microsoft has instructions here:

http://windows.microsoft.com/en-us/windows-10/create-a-recovery-drive

I'm happy to provide this as a service for my users when working on their computers. I try to always keep a number of USB flash drives available in stock for this purpose.