IF it only happened recently id check what you changed recently. heck it could even be a virus.
Also note that new Renewal clients are shit ass optimized and will sap everything out of your CPU and (probably) GPU aswell. What you can try is to install another private server that is running on pre-renewal with a pre-renewal client and see if it crashes/Turns off. If it still does. It must be something driver related, since other games dont crash it seems unlikely to be hardware.
Ok... Ragnarok Non renewal didn't crashed/turned off my pc.. So... Ideas?