hi! I really need help, i updated my macbook (pro retina 13" mid 2014) from OS X Yosemite to OS X El Capitano 10hours ago. It was working fine not after i restarted my laptop. While i was browsing on safari my macbook suddenly hanged(The only app that was running is Safari). I turned it off and right after that it's not working!!! It only shows an image of a folder with a "?". What happened? What should i do?