Ok. So I have an iMac 4,1 17" 1.83CD. My issue is, sometimes when I shut it off (say overnight), it won't turn back on. It's not the switch, because that works. I'm wondering, will the PRAM battery do that? I just replaced it, and it would not turn on for about 2 hours, but now it is turning on. Is it possible that the computer just had to reset itself after I replace the battery (and thats why it wouldn't turn on for a couple hours), or should I look deeper into something else like the power supply? Thanks!!