I ended up with a no boot device black screen after switching my laptop back one after several weeks. I tried to follow Dell support instructions but no luck so far.
I am running ubuntu 14.04.
From the Bios menu, switched the boot mode from Legacy to UEFI and restarted. I get a initiramfs prompt, after typing reboot, GRUB is displayed and if I choose the top Ubuntu option I get a kubuntu screen followed by the initramfs prompt again.
I also run Diagnostics and all tests passed (in particular Hardware scan complete with no issues)