I was using firefox today (all I had open was facebook and gmail) and iCal was open in another space. All of the sudden my macbook screen went black, but the backlight was still on and the music was playing. I hit the space bar a few times and moved around the mouse and the screen came on for a second or 2, but then went black again. It wouldn't come back, so I had to hold down the power button. When it restarted, everything was normal, except that now the fan is going fast and loud, and my computer is getting hot with only firefox open to macrumors.