Hi, just a comment as you appear to have solved the problem. If you use the run dialogue you cannot elevate a cmd prompt, you can if you use the new task run dialogue which gives an option to run any program with administrative permissions.
In win 10 if you type:- cmd into the search box then press shift+ ctrl+ enter an elevated cmd prompt will open.
In normal mode the bootrec cmd is not available (only bcdedit is) you need to access the RE (recovery environment) if able to boot to your computer (as you were able) you can easily access the RE by pressing and holding the shift key while clicking on restart. Win 10 also offers a fall back option to access the RE, if you start your computer and wait until windows starts to load then "hard" shutdown (press and hold the power button until the computer turns off) doing this more then twice windows detects a problem and boots to the RE.
Once in the RE, you need to access the command prompt. From this prompt you can successfully run the cmds, from DC3's post.
You should also be aware that in this mode windows OS will not always be allocated the drive letter C:, if you wish to access your windows OS it is necessary to find what drive letter the OS is on. I wrote this cmd to achieve this (back in vista beta days), must be used exactly as you see here:-
bcdedit | find "osdevice" (the | is called a pipe and can be found above the \ key) it returns OS device.....partition X, where X is a drive letter, typically in 10 this will be D: