ROG Crosshair X870E Extreme boot failures - Post Error / Loading VGA BIOS / QCode 62

[JPMC]

New build on ASUS ROG Crosshair X870E Extreme and have had no end of problems booting into OS, same issues also made flashing the BIOS a challenge. Unfortunately, am unable to recount the exact failure states experienced as they varied, seemingly randomly while cycling between those that initialised the display but then went blank, and those that failed to initiate the display at all.

Boot process now seems to have "stabilised" to either successfully boot, or otherwise results in only 2 error / failure states: 

Successfully boots: 

• From cold boot - initial power on, AMI BIOS page is displayed and post correctly cycles through and reaches VGA:99. LCD screen briefly flashes up "Post Error" but then Windows 11 boot loader kicks in and the system boots successfully.

Failure state 1 (alternates randomly): 

• From cold boot or hard reset - initial power on, AMI BIOS page is not displayed, and post cycles through but then stops with the code 62 and with the LCD screen displaying "Load VGA BIOS", screen remains blank.

Failure state 2 (consistent):

• Soft reboot or reset - screen displays AMI BIOS page and successfully cycles through post routines and reaches VGA:99 with a green LED but then stops. LCD screen displays "Post Error" and remains in that state.

Has anyone encountered something similar?

Have tried literally everything and in every combination to the point of not being able to meaningfully restate here. 

• Ryzen 9 9950X3D 
• ASUS ROG Crosshair X870E Extreme
• 128GB Crucial DDR5 6400MT/s EXPO I
• 1x WD_BLACK SN8100 4TB PCIe 5.0x4 NVMe M.2 SSD on M.2_1
• 2x WD_BLACK SN8100 2TB PCIe 5.0x4 NVMe M.2 SSD on M.2_2 and M.2_3
• 1x acer Predator GM7 4TB SSD, M.2 2280 PCIe Gen4x4 on Q-DIMM.2
• RTX 5080 Founders Edition on PCIx16(G5)_1 @ x8 lanes

[n0pslide]

Finally I see a fellow WD_BLACK SN8100 operator:) F#ck samsung 9100. On another note, have u tried removing the 5080, sticking an HDMI into the MOBO port and booting using iGPU?

[st3inerd]

Also if you have not already pull the qdimm board and see if that makes a difference... but it's looking like you are lane limited and its picking and choosing what it wants to do depending on power in state.  your maxing out your lanes for sure but hey try trimming it down to the basics and build from there.

[gupsterg]

Your motherboard supports flashback, I would use that method to flash BIOS, that is best method in my opinion.

128GB on EXPO I at 6400MT/s is unlikely to function, this is your most probable cause for issues you are encountering for erratic POST issues.

[JPMC]

Thanks, purchased another motherboard of the same model and had no problems at all. 

RMA'd the first board as there was must have been something faulty with it.

Am OC 128GB on Expo with optimisations and manual settings at 6400MT/s without a problem. 

Have also added another acer Predator GM7 4TB SSD, M.2 2280 PCIe Gen4x4 on Q-DIMM.1. 

So am definitely maxing out all available lanes / I/O.