Help please: Doesn't post, and mobo CPU LED switches off weird

[dinidu]

My computer just refused to post at one point. I've been using it for around six months now (GPU much older - maybe a month after launch).

 

Not OCed. GPU slightly undervolted to keep noise in check. Noctua NH-L9i 17XX cooler.

 

The board has four diagnostic LEDs. When I hit the power button (one exception I'll list later) the CPU LED turns for, then the RAM LED turns, then the GPU LED turns red, and then the CPU LED turns on immediately as the RAM led switches off and almost immediately does a fade-out kind of switching off (like how a filament bulb will switch off). The exception is if I remove the EPS cable, in which case the CPU LED stays on.

 

Things I've done so far:

 

1) Clear CMOS, checked cables, connections, reseated RAM.

2) All parts in place switch on - CPU fan powers up. GPU light powers up, no signals, and then switches off after LED sequence.

3) No GPU switch on - CPU fan powers up, VGA signal, switches off after LED sequence.

4) Flashed BIOS to F6, F11, and F20 versions through Q BIOS Plus with no CPU/RAM in place (renaming the file to gigabyte.bin) and did above steps after flash completion and CPU/RAM installation, same result.

5) Flashed BIOS to F6, F11, and F20 versions through Q BIOS Plus with no RAM just CPU in place (renaming the file to gigabyte.bin) and did above steps after flash completion and CPU/RAM installation, same result.

6) Flashed BIOS to F6, F11, and F20 versions through Q BIOS Plus with CPU/RAM in place (renaming the file to gigabyte.bin) and did above steps after flash completion and CPU/RAM installation, same result.

 

The exception is when I try boot with EPS cable removed. Then the CPU light just stays on. 

What irks me is how the CPU LED trails off instead of switching off. I'm planning on taking the system to check with a different CPU on next working day, but wondering if anyone knows what the issue could be. I've embedded video of 'full system' switch on LED behaviour.

 

My specs - A 12700K on a Gigabyte Aero G DDR4 running 2x 3600MHz TeamGroup 32GB sticks, and a Gigabyte Vision 3080 (10GB, no LHR), and a Sabrent 2TB PCIE Gen 4 SSD.

 

 

[Applefreak]

So you are getting Red lights on CPU, RAM and VGA. Unless the board is suddenly defective, have you checked with a different PSU? Also try running the system with the iGPU by removing your 3080. With everything removed but the CPU, you should still be able to enter bios with the integrated graphics. If that doesn't work, either the board, the CPU (not very likely) or the PSU remain as culprits. I'd take a close look at your PSU. Maybe it was running close to max capacity for a while with the 3080 and the 12V rails are done for. Which would result in the board still working at 5 and 3.3 Volts but it can't properly turn because 12V is unstable or non existent. So definitely check the PSU as well.

[Applefreak]

23 minutes ago, dinidu said:

undervolted to keep noise in check

Are you talking about coil whine or fan noise, which would be a simple fan speed adjustment, no need to undervolt. Just saying. 

[dinidu]

19 minutes ago, Applefreak said:

Are you talking about coil whine or fan noise, which would be a simple fan speed adjustment, no need to undervolt. Just saying. 

Both temps and fan noise. I live in Sri Lanka where the ambient in 29°C, so my room turns into an oven when I'm using the GPU.

[Applefreak]

3 minutes ago, dinidu said:

Both temps and fan noise. I live in Sri Lanka where the ambient in 29°C, so my room turns into an oven when I'm using the GPU.

Makes sense.

[dinidu]

1 hour ago, Applefreak said:

So you are getting Red lights on CPU, RAM and VGA. Unless the board is suddenly defective, have you checked with a different PSU? Also try running the system with the iGPU by removing your 3080. With everything removed but the CPU, you should still be able to enter bios with the integrated graphics. If that doesn't work, either the board, the CPU (not very likely) or the PSU remain as culprits. I'd take a close look at your PSU. Maybe it was running close to max capacity for a while with the 3080 and the 12V rails are done for. Which would result in the board still working at 5 and 3.3 Volts but it can't properly turn because 12V is unstable or non existent. So definitely check the PSU as well.

Tried with the GPU removed with thr current 750W PSU and a 650W PSU I had sitting around (both Corsair). Still the same.  Have a sinking feeling it's the CPU cos I managed to flash the BIOS