Hey guys, I have a MacBook pro that was purchased last October and has the newest os installed. I turned it off prior to leaving town for the weekend and when I returned I found that it would not start up. When I hit the power button, the white screen with the apple logo comes up and it sits on there and loads for a long time. Afterwards, a circle with a line through appears in place of the apple logo and it sits there. Any idea as to what I can do? Thanks!