I've been at this issue for several hours. I can boot into my live-usb install disk of Ubuntu 16.04 and look at the boot order, but changing it to put ubuntu first doesn't do anything -- I just boot into windows10 when I restart regardless of what I do.

https://i.imgur.com/XjQpvtW.png

I have tried a few things even from the windows command prompt, like

bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi

But that doesn't have any effect either, even though it tells me that it completes that operation.

When I boot up, I don't see any kind of boot manager that is mentioned in most threads (like grub), it just boots into win10s advanced startup. (I also used macrium reflect to backup win10)

Bear in mind that I don't actually know what I'm doing, I'm just fumbling around looking for a solution here.

Thanks very much and merry christmas :)

UPDATE: I wasn't able to solve the issue. I decided to repartition my hard drive and do a clean install of Ubuntu 16.04. Windows has been completely backed up anyway on my external hard drive and on a rescue disk.

For anyone else who finds this thread while searching: if nothing else works, perhaps try modifying the settings of your BIOS in order to allow UEFI to find your ubuntu installation.