Yesterday, I ran my Ubuntu Live CD to check if my OS partition was damaged, as I halted the computer from the Mac's button too much times. It seemed to be fine, so I restarted the computer. But now I can't boot from any Ubuntu media, when booting from the HD or the CD the screen just stays black. What can I do?
UPDATE: the CD sometimes runs and ables me to boot from HD's Ubuntu... it's surely an EFI problem.
iMac 21'5'' Late 2009
Latest version of rEFInd (after removing rEFIt)
Ubuntu 12.04 AMD64+MAC