I have a new computer with Windows 8.1 and have gone to work at dual-booting with Ubuntu 12.04.3. I can boot Windows 8 from the grub menu just fine, and Ubuntu appears on the menu and I can select it, but it will remain on a blank screen, same color as the grub menu, and does nothing, no error message. However, if I put my Ubuntu DVD in the disk drive before starting up, I can select Ubuntu from the grub menu and it always starts up perfectly.
One thing I noticed is that if the disk is NOT in the drive, I see a little message "efi disk read error" appear several times just before the grub menu is displayed. The message does not appear if the disk has been inserted. Could someone let me know what's going on?
Just following my Ubuntu install, the initial problem had been that Windows was not recognized and didn't show up in grub. I ran boot-repair (results) from my Ubuntu installation (BIOS would not boot from the optical drive after installing Ubuntu). Following this, it appeared that everything was fine - I could boot Windows and Ubuntu, and I couldn't tell you whether it was because a disk was in or not. I didn't take note of this at the time.
After this I did some various installing of software on Windows, and also got the grub menu customizer on Ubuntu to shift around my menu options, and shove some ones I don't plan to use much into folders. But that's all. And this morning I noticed that I could not boot Ubuntu unless the disk was in the drive.