Hi, wondering if anyone else ever has this issue? sometimes I come back from Uni and my iMac is on, even when its been off all day. it seems to just randomly start up. I went through the settings, making sure there was nothing set to wake the computer up (not from sleep, just to turn it on or whatev) so i'm a bit perplexed. is this a known issue? oh, its a generation back model, not the black and silver. Intel 20".