Hi, this morning while on my imac the screen went straight to black, like it went in to sleep mode but I was active at the time. Couldn't bring it out of sleep. Then couldn't shut it down. Only thing I could do was power off. When I go to start up I get the white screen for few seconds then it goes to black (no start up sounds, no green camera light) Only way that I can tell if it is off or on is by putting my ear to it. Holding down the button I can hear that it shuts down. But when I startup I get the white screen to black no startup sounds. Sometimes when I hold the start button gently I get a few seconds flash of my home screen. I've tried the trouble shooting for 'freezes' and for 'won't turn on or startup' from the manual. No luck. Anyone got any clues to what's going on, how I can fix it? (Staying calm but worried) Imac 27", late 2009, running Mavericks.