Well that's ridiculous to have to send the MB back for repair when proper diagnostics or any form of troubleshooting have not been done.
If it's still FF then yes it's an unidentified fault which can be many things.
Where the Qcode stops is your current error and Post wont continue till rectified. So where does it stop.?
If FF Qcode then you may have to Breadboard outside your Case.
Oh and btw, Your CSM (compatibility support module) should be enabled.
You stated your system boots fine on second attempt. If so then you should check your windows system files. May need a repair or fresh install.
Can I assume you installed in UEFI mode and AHCI enabled.?
You have a Bios direct key on the MB. Have you tried that.?
We owe our existence to the scum of the earth, Cyanobacteria
My System Specs:
MB:ASUS ROG Crosshair VII Hero/WiFi GPU:EVGA GTX 1080 sc PSU:Corsair AX-1200i
CPU:AMD R7 2700X Cooler: Corsair Hydro H115i Case: Corsair Carbide 780t
Memory:G.Skill TridentZ F4-3200C14D-16GTZR SSD:Samsung 500GB 960 EVO M.2
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