The newest Radeon driver keeps causing these errors. Where i wake up in the morning seeing my PC rebooted itself an i check my Radeon software an come across this. I wasn't even overclocking my GPU & i had a system failure at stock settings. Fix you're software AMD! I hate waking up to this in the morning!
You might want to check 'Event Viewer' and/or 'windows reliability history monitor' to look for what is actually causing it.