I usually use an external disk to boot MAC OS X with a 15" Mac book pro.
Now it does not work, when I try to boot as usual with Alt pressed when the computer starts, it provides the message: "You nees to restart your computer. Hold down the Power button for several seconds or press the Restart button".
When I boot with another method (the original internal HD), and I go through the Finder, I cannot see the external disk. But when I run the Disk Utility I can see the disk. I could repair it. but the volume is not mounted, and even if I try to Mount it, it tells me to repair it. But when I repair it, it tells me that the volume is fine.
I need to be able to reboot on this external disk, or at least to be able to import all data from it (that I cannot do now because I cannot see the external disk from Finder). Please advise.