My MacPro have OSX 10.6.6 and have two OSX's each on an apart Hard Disk. One system I use for the regular things and the other system I use only for video-editing. Always could I choise for the system I want on that moment, by hold pressing the "alt-key" on startup of the Mac pro, till an menu appears where I could click on the HD I want to use. Yesterday I have got an Update for OSX and have allowed to install that update. But now works the "alt-key" not more, after a while pressing the alt-key the Mac do nothing, everything stays black. Have anyone an idea how this comes and what to do on it to resolve the problem?