Unable to boot on live USB 16.04

Hi everybody,

I have a new laptop with UEFI and I am totally new to this.

Sager/Clevo
i7 6700
2 x SSD Micron
GTX 980M

I set the UEFI boot mode in the BIOS, SecureBoot on. I have Win10 already installed.

I checked the mdsum of my ISO Ubuntu image and it is ok.

When I boot on the USB key, the boot grub appeared as required by the UEFI mode.

I set the grub.cfg file as suggested in this thread : http://ubuntuforums.org/showthread.php?t=2326467

I see the ubuntu splash screen appearing (the one with the dots) and finally get to a prompt screen saying this :

[4.846284] nouveau 0000:01:00.0: gr: failed to load fecs_inst
[6.488001] sd 4:0:0:0: [sdd] No Caching mode page found
[6488018] sd 4:0:0:0: [sdd] Assuming drive cache: write through

BusyBox v1.22.1 (Ubuntu 1:1:22.0-15ubuntu1) built-in shell (ash)
(initramfs) Unable to find a medium containing a live file system

What should I do?

Thanks in advance for the help.