[Help] MSI PRO B850M-B GEN4 - No POST / No Display / No Keyboard Activity with Ryzen 9 9900X

jdepaula815ec02e8

jdepaula815ec02e8

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After switching components from a dead Asrock board to this new MSI PRO B850M-B GEN4, the system fails to POST. Upon powering on, the EZ Debug LEDs for CPU (Red) and DRAM (Yellow) light up for about 5 seconds and then turn off. However, there is no display output (tested HDMI and DisplayPort) and no keyboard activity (Caps Lock/Num Lock lights do not respond).

Steps already taken:
  1. 1- Flash BIOS Button: Can't update the BIOS using the external button and a FAT32/MBR USB drive. When I press the Flash BIOS button, the power goes on for some seconds, then turns off and the white LED blinks slow for 3 seconds, then it turns on again and the white LED begins blinking faster for several minutes with the red CPU and yellow RAM LEDs on. After that the system auto-rebooted, the EZ Debug LEDs turn on and then off, but no video signal.
  2. 2- Clear CMOS: Performed via both the dedicated button and the JBAT1 jumper.
  3. 3- RAM Configuration: Tested with a single stick in slot A2. Allowed the system to run for over 10 minutes to account for DDR5 memory training.
  4. 4- CPU Check: Reseated the CPU and verified the mounting pressure of the cooler (loosened slightly to avoid socket deformation).
  5. 5- Peripherals: Tested with different HDMI and DisplayPort cables and different monitors.
Current Status: The EZ Debug LEDs suggest the hardware check passes (they turn off), but the system seems "frozen" before initializing USB controllers or Video output. The RAM and CPU previously worked on a different B850 board.

Does anyone have experience with Zen 5 (9900X) and this specific B850 board regarding AGESA versions or specific Corsair Vengeance compatibility issues? Any advice on forcing the integrated graphics to initialize?

System Specs:
  • Motherboard: MSI PRO B850M-B GEN4
  • CPU: AMD Ryzen 9 9900X (Zen 5)
  • RAM: 64GB (2x32GB) Corsair Vengeance DDR5 6000MT/s
  • PSU: Gigabyte Gold 850
  • GPU: Integrated (testing via HDMI/DP) and Dedicated MSI GeForce RTX 3060 Ventus 2x 12G OC
 
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This is the behaviour of the EZ Debug lights...
 
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There is a new situation after you changed the PSU and did what looks like a successful BIOS flash. That means you need to test again with the RTX 3060.

What I have in the back of my mind is that the components came from a broken motherboard and will have to keep in mind other components might also be damaged. There might be minimal damage to the iGPU hence why I asked to try with the RTX 3060. What was the problem with the old motherboard?

In the video we can't see the green boot LED. Is there an SSD connected to the motherboard? Does the green LED light up?
 
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