Had overheating issues with CPU and stock cooler, upgraded the cooler to a H60, issues slowed, but continued. have recently changed out MB for ASUS 990fx V2.0. performance improved for about a week now shutting down in minutes. cpu temp in bios seems stable at 41 - 45 in bios, in windows lasts about a minute, so cannot even get temp monitor up in time to see.
41-45C with water cooling is way to high idle.. Please check that you have purchased and applied good quality Thermal paste to your CPU.
A thin layer is enough don't glob half a thing of thermal paste on there.
I would test your power supply. A temperature shutdown would log and entry in the eventlog.
We don't know that it is the PSU for certain but still worth testing. Since Popatim cannot access the Event logs before the system shuts down it's not really easy to say.