I was downloading an iTunes rental when a "cannot write to disk" error message came up. Then, everything started to freeze, so I was forced to manually restart the laptop. Instead of restarting, every time I press the power button, the gray screen comes up (without the Apple logo) and the fans go crazy. I tried putting in the OS X disk and booting up while holding down "c", but nothing happens; I also tried booting while holding "option." At this point, nothing seems to work, as I can't even boot the laptop from the OS X disk.