Idle mostly. Not even stressing the machine or anything like that. And I know it is the graphics driver, cause I could hear the fans on the cards ramp up and I would lose video but I could still use RDP (uses its own driver) from my surface to go into my machine and close things and properly reboot.While under load/gaming or just at idle? My PC has been randomly rebooting when idle and usually when I'm not nearby (obviously). Nothing notable in the event logs to tell me why though.
I'm running 2004 update and until that driver everything had been perfectly stable.