Question MSI Tomahawk B350: Suddenly unable to boot, need help with troubleshooting

[Molndrake]

After rebooting my computer earlier today, my computer refuses to boot. Here’s my hardware setup, which has remained untouched for six months, and has worked fine up until today:

Original setup (from 2017)
MSI Tomahawk B350
Fractal Design Integra M 550W PSU
AMD Ryzen 5 1600 Processor
Corsair Vengeance LPX DDR4 3200MHz 16GB (2x8 GB)

Added later (early 2023)
ASUS Radeon RX 6650 XT DUAL OC - 8GB GDDR6 SDRAM
Corsair Vengeance LPX DDR4 3200MHz 32GB (2x16 GB)

Here’s what I know

• The monitor works on a different computer
• The HDMI cable works
• CPU and case fans are all spinning
• The graphic card fans stop spinning after about 5 seconds (but I read online that this might be as it should, considering that they GPU is not hot at all)
• The CPU EZ debug LED lights up for about 5 seconds after pressing the power button, then goes dark; no other EZ debug LEDs lights up after that
• The MB backlight is on (red light from behind the board somewhere)
• I’m not sure if I can access BIOS, but probably not (screen black)
• I’m reasonably sure the OS doesn’t start

Here’s what I’ve tried

• Left only one RAM stick in the A2 slot
• Unplugged computer for 15 minutes
• Unplugged the computer for 8 hours
• Checked CPU fan power cable
• Swapped the graphics card for an old one I know works
• Used theHDMI port on the motherboard
• I've also tried removing the GFX card and unplugging everything except CPU+fan and one stick of RAM in the A2 slot, but the behaviour is identical: the CPU LED lights up for roughly 5 seconds, then goes dark, and no other LEDs light up whatsoever.

Nothing of this changed any of the behaviour described above. I would appreciate any help regarding what could be wrong or what I can do to figure out what's wrong. I don't mind upgrading old components, but I would like to know which component is causing the issue. If I should provide additional information, please let me know!

 

[--SID--]

Remove 3 RAM sticks (leave one in A2), remove storage, reset motherboard BIOS and try again to enter the BIOS.

 

[Molndrake]

Remove 3 RAM sticks (leave one in A2), remove storage, reset motherboard BIOS and try again to enter the BIOS.

I had tried all that before posting, except for resetting BIOS. I've now tried that, following the instructions here, but unfortunately, the result is exactly the same. CPU debug LED comes on for 5 seconds, then turns off. No other debug LEDs light up.

One thing I'm not sure about is if the monitor will work on the motherboard HDMI port, as I've never tried this. Right now, the computer is running without the graphics card. Should I try putting it back in? I'm asking because I'm not sure how I would know if I get into the BIOS if that port doesn't work (I've never had reason to use it before).

 

[--SID--]

One thing I'm not sure about is if the monitor will work on the motherboard HDMI port, as I've never tried this.

No, Ryzen 1600 has no iGPU so no output on the motherboard video ports.

 

[Molndrake]

No, Ryzen 1600 has no iGPU so no output on the motherboard video ports.

I see! I tried putting the graphics card in, but no luck. Same result as before. I posted elsewhere online, and somebody said that the PSU I'm using is old (I know that, of course) and has known issues (which I didn't know).

 

[--SID--]

and has known issues

What kind of issues?

 

[Molndrake]

Low-end PSU from 2014 with three years of warranty, and it has been found to lack OPP/OCP (OverPower / OverCurrent Protection). This is long overdue to be replaced.

That's what they said. I have not noticed any issues until now. My computer has suffered occasional spontaneous resets, but not very often and I've never figured out the cause. It could be completely unrelated, of course!