Hi holst01, welcome to 7F!
Couple of items to look at/try:
- Does this happen when your machine is plugged into the power supply? Try shutting down while on battery only.
It may be a bad PSU supplying too much power, preventing a proper shutdown. How old is your machine? You may have to contact Asus.
Try using another power supply if you have/can get one.
- How is your Wake-on-LAN set? There may be two settings, one in your BIOS , the other in the Operating System, this link will show you both: ASUSTeK Computer Inc. -Support- If it's on, disable it to test.
There are also reports of loose or broken grounds that can cause restarts.
I see DavidW7ncus has replied about the wake-on-lan while I was compiling an answer.
If you don't have one in the BIOS check the OS setting in Control Panel\All Control Panel Items\ Device Manager\ Network Adapters.
After your last answer, We may have to call in the Ghostbusters!