Question System not showing signs of life, PSU and motherboard appear to be working

[clubby789]

Yesterday my PC failed to boot, with only the main CPU fan and front light turning on. After a lot of troubleshooting I switched out all parts to a spare (and unused) motherboard, CPU, GPU, RAM and power supply.

I was able to boot into WIndows once. However, after shutting down, the PC is showing no signs of life when the power button is pressed. No fans spin or lights turn on.

What I've tried:

• Using a screwdriver to connect the power switch headers
• Doing the paperclip test on my PSU (shorting pins 4+5 and plugging it in, the PSU fans started spinning as usual)
• Changing the wall socket and power lead used for my PSU
• Connected a simple USB lamp (the lamp turns on, both when connected to the main motherboard USB and the front panel ports)
• Disconnecting and reconnecting both the 2x4 CPU power and 24-pin motherboard power several times

I have a buzzer connected but no beeps have been produced, with or without RAM installed. The working lamp and PSU test seem to indicate that at least some power is making it through the PSU and onto the board, but not enough to begin booting.

I'm worried that a connected peripheral has somehow damaged both motherboards, but I'm not sure how likely/possible this is.

 

[rgd1101]

full system spec? include brand an model of the psu

 

[clubby789]

full system spec? include brand an model of the psu

PSU: BE QUIET Pure Power L11-400w
CPU: i5-10400
MB: Gigabyte B460M
RAM: Corsair Vengeance 4x8GB 3000Mhz

 

[clubby789]

I plugged the power supply in after leaving it unplugged for an hour and the fans spun up again without me pressing the power button. There were 5 beeps but they didn't repeat. I used the switch to turn it off again and it hasn't turned on again since.