Duke has a problem with his Windows 10 computer, which is restarting suddenly out of nowhere after about 10 minutes. Leo says that processors heat up really quickly, and if the thermal paste that ties the fan to the processor has dried up, it can easily start to overheat within a few minutes. There's software that can help show you if the processor is overheating. HWMonitor is the one to get.
But the most common failure point for restarts is the power supply. If the power supply begins to fail, it will restart suddenly. Fortunately, it's easy to replace.