Ahhhhh! Sometimes when I turn my iMac on, it'll start doing its thinglight comes on, chime goes, fan whirrs, but then it'll make a strange click/"werrrrh" noise and turn off. It's happened twice to me since I've brought it home from school and each time I just tilted the monitor around while turning it on and it worked. I have been avoiding turning off / restarting my computer because I'm afraid its going to happen and I won't be able to get past it. Could the powersupply be loose or something? I really have no idea!