I know the answer to this question will likely be just get a new computer, but I've got an 8 year old iMac that suits our purposes perfectly. I really don't want to blow another couple grand just yet. I've got it backed up so I'm protected. Anyway, I don't know the events that led up to this, I have 2 young kids. But the computer simply won't turn on. It will begin the start up procedure. I'll get the white screen with apple logo. A little progress bar appears at the bottom of the screen as normal. About 3/4 of the way through the start up process, it all of the sudden just shuts down. I mean completely powers off. So far the only trouble shooting I've done is to unplug it, hold the power button down for 10 seconds, plug it back in still holding the power button for 10 more seconds and then finally releasing the power button and then pressing it again as a normal start up. The only difference this makes is the cooling fan turns on full blast as it starts its power up procedures. But it will do the same thing, get about 3/4 of the way through the progress bar on the white screen with the Apple logo then suddenly completely shut down. Any thoughts or trouble shooting tips? Thanks! I replaced the mother board or logic board or whatever you call it these days about a year ago.