I was playing a game on my 20" Aluminum iMac (first gen) in windows vista, and it bluescreened and crashed. I shut it down, booted it up again, and it won't work. When it starts up, it makes the tone sound, but is black at first. Then the screen turns on grey, and after a few minutes of waiting a gray folder with a question mark on it is blinking. I've tried rebooting several times only for the same thing to happen. How can I resolve this?