Hi everyone, I'm new here and I tried searching for someone with a similar issue, but wasn't able to find anything that sounded quite like this. I've been living with this problem for years, by just keeping my computer on at all times with it set to never sleep, and avoiding shut downs unless I must do them. The Problem: Starting sometime in 2011-12 I noticed that when I'd shut my computer down, it would almost always freeze upon restart. When I say freeze, I mean that the mouse wouldn't move and everything was unresponsive. Usually I'd have to power it down by holding the button, but sometimes it would crash and restart itself and a grey warning screen would come down. I was told by Apple Care to reinstall my OS which I did at the time, but it never truly solved the problem. More Detail: the time it takes for it to freeze up seems to be anything from 1 minute of operating time after reboot up to 10 hours in one occasion, where I had thought the problem had gone. I fired up a youtube video and a little bit into the video, it froze. Strangely, it often seems to freeze after reboot/sleep during a youtube video. Not sure if that is coincidence or indicates some kind of graphics/video problem. Additionally, I sometimes use Bootcamp to run Windows 8 and have had it crash similarly and needed to force a restart after having the computer shut down, and running Windows. This makes me suspect that it could be a hardware issue rather than an OS issue, but I don't know a whole lot about computers. My Computer: Mac Pro (Early 2009) 2 x 2.26 GHz Quad-Core Intel Xeon 8 GB RAM Graphics NVIDIA GeForce GT 120 512 MB It has no aftermarket anything inside of it. I did recently order a new PCI SSD hard drive for it, but it hasn't arrived yet. The thought of shutting my computer down for this purpose made me think of asking some smart folks like yourselves. Any advice on diagnosing this issue would be greatly helpful! Thanks to all!