For the last week my late 2013 27" iMac (fusion drive fwiw) has several times when in use shut down entirely. It's like the plug is being pulled, just poof. It isn't just the display, the connected USB drive dies too. When it happens the power button doesn't work. You can hold it for mnutes, push it once, whatever and the iMac won't power back up. To get it to restart I have to physically unplug the plug from my surge protector and plug it back in. I've tried multiple outlets with the same results. Today it has happened 7 times so far, by far the worst yet. There is no rhyme or reason to when the shutdowns occur. I've had it happen when sending an iMessage, using Firefox, browsing a file folder, watching a YouTube video, etc. I have AppleCare and called this morning but wasn't really helped much. He had me flash the RAM and said since I can't reproduce it with an action there wasn't anything he could do. An ideas what might be causing this? There have been no changes to the machine, it's entirely up-to-date, and doesn't have any crazy apps or anything. Just standard Adobe CS, FileZilla, TextWrangler, etc. Nothing rare. Thanks for any advice!