I've had this particular problem on the machine. Mac Pro 2.8 quad. Until recently it only had 3GB ram. I switched the hard drives into my other MP quad 2.66 and it never had a problem restarting. I just dropped 32 GB ram and installed a X5690 CPU in the Mac that doesn't restart. I didn't do that as a solution to the restarting problem; but you know, I thought it might fix. It didn't. It didn't USED to have this problem. I think it started when I went to Yosemite or maybe the previous OS but I can't pinpoint it exactly. What should I look for to fix this? What can this be? When I select restart or shutdown all the applications close and then it just sits there without shutting down or restarting. I have to manually shut it down by pressing the button in front.