Z370 Cold boot issue

It sounds alot like an Issue I had with my Asus X99 Board , it was caused by the way the Board's xHCI Controller and how it handles USB at Boot, in particular USB2 Hubs and Devices , eg some Joysticks.

In my case it turned out to be the USB HUB in my older NEC Monitors which I wasn't able to get a Firmware update for , so I just stopped plugging it in , another USB HUB I have I was able to get a newer Firmware for , so it then booted correctly.

found this on OCUK back then , but nothing changed the issue until the suspect device was removed at boot.

This is a better explanation of the xHCI settings.

"XHCI Mode = Disabled
The on-board USB 3.0 port function like a 2.0 port

XHCI Mode = Enabled
The on-board USB 3.0 port function like a 3.0 port

XHCI Mode = Auto
The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load.
If you reboot the OS, the on-board USB 3.0 port again function like a 2.0 port during this reboot BIOS phase before OS USB 3.0 driver load.

XHCI Mode = Smart Auto
The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load.
If you reboot the OS, during this reboot BIOS phase, BIOS is "Smart" enough to avoid downgrade the USB 3.0 port back to 2.0 functionality before OS USB 3.0 driver load. So Smart Auto is faster than Auto on 2nd boot onward, but Enabled is fastest once you are sure the OS has the USB 3.0 driver installed, because it avoid the switching. Making the on-board USB 3.0 port function like a 2.0 port is mainly to support OS installation or to support OS that does not have build-in USB 3.0 driver, so that the USB keyboard would still work if the user plug-in a USB keyboard or any other USB devices into the USB 3.0 ports before the OS is installed with the USB 3.0 driver come with the motherboard."

Thanks for the info Kbird I shall look in to that

Cheers Kbird, that's very informative so whilst I hope it resolves the OP's issue, it has also educated my own journey with USB issues on my X79.

Watching this thread with keen interest!

Good luck

Hope it helps guys, just to be clear this was not a Asus issue only , my 1st X99 Board was a Gigabyte which I now think had the same issue but the Store thought it had other issues and even swapped out my Ram before swapping it for an Asus X99A which had the same issues , so they gave me the X99A-USB3.1 which died , a 2nd one of them died and took out the CPU too , so I refused another as I knew the X99A-II was about to hit the Market and although it had the same issues ( I later determined the issue was infact this USB xHCI thing) it has been okay except for the disappearing Logitech Mice and Keyboards Issue some have and the last Bios didn't fix ( for me) as reported.

I have read the X79 series was similar but I am not familar with them , my previous MB was a X58A series.

I had a look in the bios/advanced usb config and there is no option for XHCI mode.

essenbe said:

Do you have USB Legacy set to enabled?

I'm pretty sure it is but will check

Edit: Yes its set to enabled

essenbe said:

Did you get the new ram yet? Also, has that board ever run right?

No mate it won't be here until Wednesday. As for the board it's the 2nd one I've had that and no its never run right. Both have done exactly the same things.