Repair disk failed
Hello kind people,
Since I upgraded my OS to El Capitan, my internal disk gave me headache. Suddenly I can't get in into the system, which I mean when I turn on my laptop, the logo comes, then loading for long time before it turns off. I redid and same thing happened. I can't log in. Then I tried to go Disk Utility, repair but it is failed. From what I know I can erase my hd, format then reinstall but it also means I will loose all my super important data. I don't want it.
What should I do? How could I restore my data to external disk from disk utility?
Thank you very much. I appreciate a lot.