Question New PC won't boot (B550 Gaming Plus Mobo) - CPU debug light and no monitor display

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Dank Chi

Dank Chi

Jan 14, 2025
5
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I recently purchased all new parts but having trouble booting up the PC. All LEDs and fans turn on (including peripherals) but the CPU debug light is on and no monitor display (black screen).

What i've tried:

  1. Flashing BIOs via latest non-beta BIOs with FAT32 USB and mobo bios flash button (flashed red for approx 5 min then PC restarted on its own but still CPU debug light and no display)
  2. ^ tried flashing BIOs with different FAT32 USBs
  3. Reseated CPU on mobo with correct pin allignment
  4. Tried different CPU pins on PSU
  5. Tried booting from mobo display port instead of GPU (GPU removed)
  6. Reset CMOS via jumper and battery removal (2-3 min)
  7. Tested CPU on different PC and it worked
  8. Tested PSU on different PC and it worked
  9. Confirmed AIO fan pins are connected to "CPU FAN" and AIO 3-pin is connected to "PUMP FAN"
  10. Swapped CPU PSU cable
PC specs:

  1. Ryzen 7 5700x3d
  2. RX 7800 XT
  3. MSI B550 Gaming Plus
  4. DDR 4 RAM 64GB
  5. Crucial P3 Plus M.2 1TB
  6. Thermalright Frozen Notte 240 AIO Cooler
  7. Corsair RM850x PSU
Any ideas on what i can try next?
 
Dank Chi said:
I recently purchased all new parts but having trouble booting up the PC. All LEDs and fans turn on (including peripherals) but the CPU debug light is on and no monitor display (black screen).

What i've tried:

  1. Flashing BIOs via latest non-beta BIOs with FAT32 USB and mobo bios flash button (flashed red for approx 5 min then PC restarted on its own but still CPU debug light and no display)
  2. ^ tried flashing BIOs with different FAT32 USBs
  3. Reseated CPU on mobo with correct pin allignment
  4. Tried different CPU pins on PSU
  5. Tried booting from mobo display port instead of GPU (GPU removed)
  6. Reset CMOS via jumper and battery removal (2-3 min)
  7. Tested CPU on different PC and it worked
  8. Tested PSU on different PC and it worked
  9. Confirmed AIO fan pins are connected to "CPU FAN" and AIO 3-pin is connected to "PUMP FAN"
  10. Swapped CPU PSU cable
PC specs:

  1. Ryzen 7 5700x3d
  2. RX 7800 XT
  3. MSI B550 Gaming Plus
  4. DDR 4 RAM 64GB
  5. Crucial P3 Plus M.2 1TB
  6. Thermalright Frozen Notte 240 AIO Cooler
  7. Corsair RM850x PSU
Any ideas on what i can try next?
Click to expand...
Did you try memory? What slots are they in and did you make sure they are seated correctly?
 
Last edited:
Notmiserable said:
We don't know if BIOS is updating correctly without display. Have you tried a different USB drive?
Click to expand...
yes, tried it with an old USB (2.0 i think). same thing happened - BIOS flashback starts flashing red, turns PC on and continues to flash red for approx 5 min, then restarts the PC and stops flashing, but CPU debug light is still on and display wont show. im starting to think my mobo is faulty, but im all for any last suggestions before i return it and buy a different mobo
 
Dank Chi said:
yes, tried it with an old USB (2.0 i think). same thing happened - BIOS flashback starts flashing red, turns PC on and continues to flash red for approx 5 min, then restarts the PC and stops flashing, but CPU debug light is still on and display wont show. im starting to think my mobo is faulty, but im all for any last suggestions before i return it and buy a different mobo
Click to expand...
Did you try everything bare bones, like everything disconnected that's not essential to flash it?

Maybe even try with one stick of ram. Try it without flashing the bios update. Just on the A2 slot. Maybe try other slots as well. See if anything changes.
 
Notmiserable said:
Did you try everything bare bones, like everything disconnected that's not essential to flash it?

Maybe even try with one stick of ram. Try it without flashing the bios update. Just on the A2 slot. Maybe try other slots as well. See if anything changes.
Click to expand...
ok ill try that since i might as well strip it down if it doesnt work and ill have to replace it.

what's all essential to flash it? im assuming mobo + cpu + cpu cooler + 1 RAM stick in A2 + PSU?
 
Dank Chi said:
ok ill try that since i might as well strip it down if it doesnt work and ill have to replace it.

what's all essential to flash it? im assuming mobo + cpu + cpu cooler + 1 RAM stick in A2 + PSU?
Click to expand...
Before that you can try 1 stick of ram (try A2 slot and B2 slot), clear cmos battery for 5 mins, unplug computer and take out battery. Give it 5 mins and see if it displays.


It doesn't need CPU and Memory according to the manual to flash update. Page 33

Updating BIOS with Flash BIOS Button
1. Please download the latest BIOS file that matches your motherboard model from
the MSI® website.
2. Rename the BIOS file to MSI.ROM, and save it to the root of your USB flash drive.
3. Connect the power supply to CPU_PWR1 and ATX_PWR1. (No need to install CPU
and memory.)
4. Plug the USB flash drive that contains the MSI.ROM file into the Flash BIOS Port
on the rear I/O panel.
5. Press the Flash BIOS Button to flash BIOS, and the LED starts flashing.
6. The LED will be turned off when the process is completed
 
Last edited:
Notmiserable said:
Before that you can try 1 stick of ram (try A2 slot and B2 slot), clear cmos battery for 5 mins, unplug computer and take out battery. Give it 5 mins and see if it displays.


It doesn't need CPU and Memory according to the manual to flash update. Page 33

Updating BIOS with Flash BIOS Button
1. Please download the latest BIOS file that matches your motherboard model from
the MSI® website.
2. Rename the BIOS file to MSI.ROM, and save it to the root of your USB flash drive.
3. Connect the power supply to CPU_PWR1 and ATX_PWR1. (No need to install CPU
and memory.)
4. Plug the USB flash drive that contains the MSI.ROM file into the Flash BIOS Port
on the rear I/O panel.
5. Press the Flash BIOS Button to flash BIOS, and the LED starts flashing.
6. The LED will be turned off when the process is completed
Click to expand...
CPU debug light still on. it cant be the CPU tho since it works on my other PC. will replace the mobo tomorrow. thanks for the help anyway 👍
 
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