Intel does not have drivers for Windows 8.1 for the 82583V LAN. Only Windows 8. Windows 8.1 has in-the-box drivers for the LAN which should work fine. I've had no issues with the drivers on my system, probably something else causing your issue.
Windows 8 and 8.1 have most, if not all, of the drivers built in and are more current than the ones Asus has available.You can get AMD chipset drivers here:http://support.amd.com/en-us/download/chipset?os=Windows+8+-+64You can find more current Asmed...
Do you have any USB ports connected to the headers on the board such as front ports on a case? It was a internal USB hub like that which was causing my issues. Also try disabling sound, Ethernet, etc to see if that fixes it. I doubt it would be the B...
As I stated in my other post, I would bet it is a hardware issue somewhere. I would start by disconnecting all USB devices you can. I had a USB hub that would cause my computer to freeze when it attempted to go to standby.
I don't have the Z but the option doesn't exist in the non-Z, or many other motherboards either. It is pretty much a standard thing now with no option to enable or disable it.You can see if the S3 state is available in Windows by typing "powercfg -a"...