Black Screen with Cursor

Hello,

I have a Dell Inspiron 1545 running Windows 7, and it just randomly turned off while using it the other day. Now whenever I try to turn it on, it loads the Dell screen, but after that just goes to a black screen with a cursor and the Windows screen never loads. I've hit F12 and run diagnostics on it but it says nothing's wrong. Please help! Ideally I'd like to keep the stuff on my hard drive, but if i have to lose it to get my computer to work again that's okay too.