This message was posted on behalf of Intel Corporation
In this case we can try to install Windows® 7 using the F10 method.
First we need to make sure the SSD is showing under boot devices in the BIOS, if that is the case then it is being recognize properly, if it is not listed then make sure it is properly connected on the M.2 slot.
Turn the NUC off connect the bootable USB and turn it on, as soon as it is starting up, press F10 several times and you should get the boot menu, just select the USB form that list and Windows should get installed on the NUC.
Make sure to enable both Legacy and UEFI on the BIOS.
The problem could be related to the image on the USB or to the USB itself, so if you can use a different USB that will be useful and we had cases where the customers use the following link to create the USB bootable device and it works fine, in case you want to try that here is the link:
There is no reports of a know issue with the EVO 850 SSD, but I found a forum that recommends to get some drivers for the installation of Windows® 7 to get completed:
If you cannot get those drivers, then please get in contact with Samsung about this problem:
Samsung’s phone number: 1 800-726-7864
Samsung’s support site: http://www.samsung.com/us/support/
NOTE: These links are being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.
Any questions or if you need further information about this matter, please let me know.