Sorry for my English but I try! I have a iMac 27 "3.1 GHz Intel Core i5 from mid 2011.12GB memory. For a week I had problems with the image on the screen was staggered when I was working.The image flickered too. It disappeared after two restarts, and then the next problem was that the computer shut itself down after ca. 10 min of using. Sometimes I could not even login. Come to the image of the apple and the bar loaded, but then it became white and the computer rebooted. During this period I installed Il Capitan in the hope that it would solve the problems. It did not. Now it has gone so far that I can never login. Coming to the screen for the apple and, the bar being loaded, and then it will be white. And then the computer restarts. I have tried with wired keyboard: Starting in Safe Mode: not working Reset the NVRAM: not helping Keeping alt down at startup: can select the network and to restore the hard drive, but after that nothing happens. Keep D pressed on startup: get error code 6000D Keep cmd + alt + r pressed at startup: the same error 6000D Keep cmd + r / alt + r: nothing happens Keep cmd + alt + p + r: nothing happens Can I do anything else? I have some files that I do not have backup. Works program like DiskWarrior and / or Boot Rescue if it´s starts from the USB stick? Which is the best?