Today I had my first frustrating experience in mac, since I made the switch, many years ago. After running and uninstalling(with its official uninstaller provided) autocad 2013, my mac went away! After a reboot, it never boot again. It stacked in the boot screen, in the grey screen with apple logo and the circle below. I booted into recovery hard disk option, and I made repair permissions and repair disk. For the first time in my life I saw repairing to last about 20 minutes, in ssd drive! But, even after this task, it did not booted. The only thing that saved me was my superduper backup. I made a restoration and now my mac works again. I really cannot understand what happened, so if anybody has a clue, please tell me. Also I would like to know about the option of re-installing lion. Can I make a recovery boot dvd of lion? Can this help me in the future in a case like this one? Will I keep all my files and settings after a re-installing of lion? Will it go back to a previous version of lion? If I had 10.7.4 and dvd disk has 10.7, will I have then, a 10.7 system and so I will have to download all updates from the start? I would like to have your comments about what could have happened to my system, and about recovery disk of lion.