Hey all, My iMac (late 2012, 21.5") suddenly started having trouble booting this past week, and I'm a little worried, as I have upcoming deadlines that are pretty urgent. In most cases, it won't even reach the white startup screen — after pressing the power button, the screen stays black, and I'm only able to tell it's "on" because my external hard drives light up, and because I can hear a very faint fan noise from the iMac itself. I've successfully booted several times now with a simple SMC reset (unplug for 15 seconds, plug back in, wait 5 seconds, power on), but this doesn't seem to be working today. Even if I do manage to boot up today, I'd still love to know the possible causes of this. I really don't want to have to buy a new Mac. Any ideas or suggestions welcome. Thanks so much!!