I have a toshiba p850 laptop with ubuntu 14.04 (used to be win 8\ubuntu).
Everything worked fine for many months. I mistakenly changed the boot mode from uefi to cms and ubuntu doesn't boot.
Of course, after realizing the mistake I set the boot mode in the bios to uefi again. Unfortunately, all I get is a message saying: reboot and select proper boot device or insert boot media in selected boot device and press a key.
Secure boot is disabled and I loaded the bios defaults...
I'm quite positive im booting the HD, in my laptop I can even select this at boot time.
If it helps, my screen doesn't even get red-ish as it used to just prior of booting into ubuntu.
Ok this may help someone. I downloaded an Ubuntu image in another computer and prepared a bootable USB. I booted my laptop with this USB and then installed boot-repair. This little program solved the issue.