Howdy folks, I'm hoping for a little guidance here. OS X 10.6.8 2009 Mac Pro (4,1) 8 core 2.26 20 GB RAM Radeon HD 4870, dual monitors Samsung 840 PRO SSD, 4 spinning hard drives The most recent hardware changes were an upgrade from 12 to 20 GB of RAM and the SSD boot drive but that was back in December. In the past I've occasionally had my Mac freeze while playing Team Fortress 2. When this happens the mouse still moves but I can't get anything to change on the screen. I can SSH in and see the WindowServer process is "stuck." I can reboot the machine over SSH. In the past few weeks my computer has started freezing more frequently. While it has happened in TF2 it has also happened while scrolling webpages and today watching the WWDC stream. Much more light duty "office stuff." These freezes kill the machine completely. The mouse doesn't move, the screen is frozen. The computer doesn't respond to pings and is dead on the network so I can't even connect via SSH to see what the issue might be. Holding down the power button is the only fix. I've let it sit for 30 minutes and it never unfreezes. I wondered if it might be the SSD so I've booted off a clone of my boot partition on a spinning HD and un-mounted the SSD. It still froze. I think that is enough to rule out the SSD? My initial thought is the video card. It always seems to happen when there is motion on the screen and occasionally before it happens scrolling or motion gets really choppy. One time the screens flickered a lot after the hard-restart but only that once. I'm not anxious to spend $500 on a new video card unless I'm pretty sure that is the issue. So, any thoughts? Any tests to try? Any certain log file I can check after the next freeze/hard restart? I appreciate any and all help.