I found after a physical move I had to readjust all my overclocking settings. Not sure why but the settings which used to be stable no longer are. I find the less I disturb the rig itself and the less downtime it has, the more stable it is. Starting it up again after downtime is the most precarious time of all and when I've had hardware failures as well.
Same. I had a rig that ran for just over 2 months with no issues. I rebooted the host rig and on reboot I had 7 of 8 GPU cores. That 8th core never came back regardless of how much crap I tried. I think I've had 4 5970s die this way. I'm down to 12 5970s and I'm determined to only shut them down when I plan on permanently shutting down.