Server Rebooting under High CPU Load

Whenever I do a task which is heavy on the CPU, my server will reboot after a few minutes. This happens regardless of what processes are running, it happens when Plex is transcoding or if I use the stress bash command. Most of the time it reboots back into QuickBox but sometimes I have to force a hard reboot in the servers control panel.

that sounds like a hardware problem the heat could cause to reboot…
just a thought.

Yeah, I thought that but the CPU never goes above 50C.