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Z790 Hero, strix 4090 - sometimes black screen on boot

Level 9


I have Asus Maxiumus Z790 Hero and Asus ROG Strix GeForce RTX 4090, i9-13900K CPU. BIOS 1501.

Sometimes I have black screen on boot(it happens about 1 in 10 cases). The problem occurs only when the Launch CSM BIOS option is disabled. The monitor is connected via HDMI cable to the video card. When this problem occurs, the white Q-LED comes on and does not go off and Q-Code LED shows code D6.

This is quite annoying because I can't turn on ReSize BAR when CSM is on.

Is there any way to fix this?


Level 17

My last PC, a 9900, used to swap video output when CSM was turned on, so perhaps that what's happening in your case as well. Maybe it will help if you turn off internal graphics, rather than having it set to auto. I'm not sure, but maybe worth a try. 

The signal might also be swapping to another video port on your GPU. I used to have two monitors, both on the same GPU (I think). If it's that, then then I'm not sure how you can stop it from doing it, but perhaps there is a way.  


Z690 Hero, BIOS 3101, MEI 2345.5.3.0, ME Firmware, 7000X Case, RM1000x PSU, i9 12900K, ASUS TUF OC 3090TI, 2 x 16GB Corsair RAM @ 5200MHz, Windows 11 Pro 23H2, Corsair H150i Elite AIO, 4x Corsair RGB fans, 3x M.2 NVME drives, 2x SATA SSDs, 2x SATA HDs.

First of all, the problem occurs only if CSM is disabled.

I am using only one monitor.

Well, there is another problem. When the Primary Display is set to PEG Slot and CSM is disabled this problem occurs every time (white Q-LED and black screen).


What VBIOS are you running?

13900KS / 8000 CAS36 / ROG APEX Z790 / ROG TUF RTX 4090

VBIOS version: 95.02.3C.00.5D (I have attached screenshots of GPU-Z).

I have checked once again (maybe something changed between 1303 -> 1501 BIOS version).

BIOS settings:

Launch CSM: disabled; Primary Display: PEG Slot; iGPU Multi-Monitor: Disabled <--- same problem as in first post (sometimes white Q-LED and D6 Q-CODE).








Level 7

if you have GPU and Thuunderbolt both connected to the same monitor, it may show balck screen. I had this issue. When typed in password on keyborad and windows unlocked, i got picture, but windows display options showed i had 2 displays connected. Until yesterday, i figured out that mobo got into conflict which vga to use to show graphics, so it chosed thunderbolt despite my monitor was set to take signal from GPU. 

Nope, I have disabled Discrete Thunderbolt(TM) Support option in BIOS.

I'm connecting one monitor by HDMI cable only.

Level 9

I also noticed some strange difference in booting depending on whether CSM is enabled.

  • Launch CSM: Enabled; Primary Display: PEG Slot; iGPU Multi-Monitor: Disabled; Boot Option Priorities: all Disabled

If no DP and HDMI cable is connected to the RTX 4090 graphics card then the system boots normally - green Q-LED on and A9 Q-CODE. I can shutdown computer by pressing power button or reboot by pressing CTRL-ALT-DEL on keyboard.

  • Launch CSM: Disabled; Primary Display: PEG Slot; iGPU Multi-Monitor: Disabled; Boot Option Priorities: all Disabled

If no DP and HDMI cable is connected to the RTX 4090 graphics card then the white Q-LED(green too) lights up and does not go out. Q-Code LED shows code D6. After the time specified in Post Delay Time, the keyboard and power button(even pressed for 5 or more seconds) stop responding.
I can only turn off the computer by cutting off the power.

Is this normal behavior?

Level 9

Ok, I've checked the various options.

It seems that the problem from the first post occurs when I set Option ROM Messages to 'Keep Current'.

So far, after setting 'Force BIOS', the problem has not occurred. (Checked on about 50 reboots).

Level 9

Spoken too soon.

Problem still persists. XMP off - DDR5 4800. I ran TestMem5 (config Extreme1@Anta777) for 2h19m - no errors. I then restarted twice. Then I turned off and on and boom - there was a problem - only a white Q-LED, 'FB' Q-code and black screen. RAM is on the Asus QVL list.