Why does auto8 restart automatically after shutdown?

According to your description, your notebook is brand new and everything is working properly after booting. It should not be the reason for the hardware. Personal estimates should be the reason for the system setup or software.
Software, it is recommended that you restart by pressing F8, select the last correct configuration, or enter safe mode to uninstall the recently installed drivers and software.
The system setting is the most likely, win8 and win7 compared to the boot speed is greatly improved, in order to improve the boot speed of win8, Microsoft added a "mixed start" concept, is to turn the operating system into one A sleep-like state, while reducing the data write of the memory temporary storage, greatly reducing the time for the hard disk to read and initialize when booting. This is the principle of the "Enable Quick Start" function.
Workaround:
First, in the Control Panel You -> Power Options -> System Settings, find the "Shutdown Settings", remove the "Enable Quick Start (Recommended) & rdquo; Select, this will solve most of the problems after restarting win8 shutdown.

Second, the appearance of restart intermittentity may also be to allow hardware devices to wake up the computer. Open the device manager of the computer, right-click on the mouse at the mouse, find the power management option, disable this feature, and also disable the keyboard, touchpad feature.