My laptop won't boot!!!

Hello,
I was using my laptop and then it suddenly shut off. I tried to turn it on again, everything was working as normal, like the logo name screen came up and all. But then it went to a black screen that had an underscore in the top left corner that kept blinking. I though that maybe if I left my laptop on for a while it would load, but it didn't! I could still hear the fan spinning amd everything working. Tue cap lock light even came on when I pressed it! I don't know what's wrong and I'm going out of my mind since I have important files on my laptop and everything for school!

My laptop is an Asus K53S model windows 7. PLEASE HELP ME!