Hello Konig, welcome to the ROG forum.
Do you have the 8-pin cpu power cable connected at the top by the 4-pin? Connect it if you don't.
You might have windows set to "check for windows updates only" which is how I prefer it. I like to know what motherboard drivers are being installed and if they are the latest drivers.
The maximus viii extreme should have came with Kaspersky antivirus on the motherboard disk, you could use that unless you're saving it for when Norton expires.
🙂Check in the device manager to see if there are any yellow triangles which would point to a driver not installed.
If everything checks out and you're still having problems, in the bios on the extreme tweaker tab set the VCCIO voltage to 1.20v - 1.25v and the cpu system agent voltage to 1.20v - 1.25v. Start with both at 1.20v first.