Hav e been troubled with random restarts for some time, at least since last major update. No warnings given no problems found with scf scannow, or malware and virus scans. Shutdown guard does not stop this or any other fix (rename reboot to .bak).No excess processor usage before shutdown. Is there a way to stop restart unless asked to?
Are all your fans working , pc's sometimes do random restarts when over heating , check your power plan to see if something has altered , check your anti virus to see if a box is ticked to restart after a scan.