What is causing my solid B.L.o.D on my PS4 Slim?

I believe I have a power issue with my PS4 Slim, but can’t identify the cause. I know it’s not the PSU or HDD. I have tried to boot it without the HDMI connected, but I still run into the same issue. Additionally, I cannot boot to ‘Safe Mode’. The PlayStation gives the initial turning on beep, blue light comes on. Freezes up for 10-15 seconds and then turns itself off.

So this leaves me with the question “What is causing this issue?”

Things to note:

- I press the power button. I’m presented with a solid blue light (10-15 seconds)

- The fan starts up for about a second, and then immediately stops

- I have tested the HDD in another PlayStation. It works fine

I have been told it might be a Southbridge issue, but I want confirmation before I start attempting to replace/reball anything.

All or any help is greatly appreciated!