I got a big big problem.. I'm using macbook with Mac OSX, yesterday I updated a firmware through software update. then after a while a black screen appeared telling me to hold down the power button to restart. when it went back, there's no login window,just a white background with a question mark folder blinking in the center of the screen. so I restart it again, and now I only get a white background and it won't start. what shall I do?? I tried inserting the MacOSX installer and doing the first aid repair, but I got an error message. I also need help on how I can back-up my files.. thanks guys.