Windows 10 No Boot Device
Ah. It's a little archaic but if you can get a hold of a burnable DVD just download a copy of Windows 10 from here http://www.microsoft.com/en-us/software-download/techbench and burn it to disc http://www.osxdaily.com/2015/11/22/burn-disc-images-os-x-finder . Once complete Make sure it's in your DVD drive then power off the Mac. Power on again and immediately hold the Option Key. Choose the Windows option and hit enter. Should boot now from DVD. I have had the same issue trying USB Windows 10 installer boot on a 2011 MBP and could only install from DVD. Good luck.