Did Windows 8 “Spontaneously” Reboot?
When certain errors occur, Windows 8 will reboot itself. This apparently random behavior is actually built in to the system in the event of a system failure—also called a stop error or a blue screen of death (BSOD). By default, Windows 8 writes an error event to the system log, dumps the contents of memory into a file, and then reboots the system. So, if your system reboots, check the Event Viewer to see what happened.
You can control how Windows 8 handles system failures by following these steps:
1. In the Start screen, press Windows Logo+W to open the Settings search pane, type advanced system, and then click View Advanced System Settings to open the System Properties dialog box with the Advanced tab displayed. ...