Hi all, I've a Mac Pro flashed from 4.1 to 5.1 which requires a 'rest' of about two hours from shutting down to restarting properly. If I restart immediately then usually get a progress bar that stops at about 75% and never progresses beyond that. I have an internal spinning disk hard drive as a backup (boot disk is an ssd), and I can hear that tinkling away long after the progress bar has stopped moving. I've learnt that if I wait for a couple of hours before turning the machine back on then then it boots more or less reliably. This was an issue before the 5.1 flash, so I think that can probably be discounted. Booting form a USB stick has the same result. I assume it's some sort of thermal cutout, but I've really no idea. The current situation is a bit more serious, I have a non flashed RX560, so I no longer get the progress bar, the screen is always blank until I get a successful boot. Now I've recently installed new X5680 cpus to fix the audio stuttering bug. It won't boot fully at all but I get the startup bong sound and the hard disk sounds the same as it did before, running for many minutes, so somethings going on but I don't know what. The symptoms seem the same as previous failed boots, but it might be the cpus or the installation. Does anyone have any ideas on what I might do to fix it or investigate further?