NUC5i5RYH boot problem USB device ubuntu

Hello,

I've got NUC 5i5RYH (HyperX Impact 8GB and SSD Samsung XP941 128GB M.2 NGFF PCIe)  without OS.
I'm trying to install "ubuntu-14.04.2-desktop-amd64" creating boot disk on USB device (using unetbootin-windows-608).
In the bios startup menu I've disabled "secure boot" and "fast boot".
I'm not able to boot the LIVE version and execute the OS installation, because the system shows this message:
"GNU GRUB 2.02beta2-9ubuntu 1

Minimal BASH-like line editing is supported. For the first word, TAB lists possible command completions. Anywhere else TAB lists possible device or file completions."

How can I fix the problem?

Thanks!
Matteo