Things have just gotten interesting. I took another look at the PC and noticed, or rather, didnt notice any LEDs on the motherboard, so I suspect the motherboard has died with the PSU. I mind as well try a new installing a new cell battery to see if that makes a difference.
In order to reach that battery I had to remove the GPU. With the GPU removed I mind as well take a clothe and remove some dust in the area I couldn't reach before.
Underneath one of the cable management panels that separate the chambers of the chassis (see picture)

I found some liquid. It was not water, and if left a residue. Wiping it with a cloth left some yellowish color on the cloth.
So now I suspect my liquid cooling heatsink had a leak, killed my PSU and my motherboard.
When I first noticed my PC wouldnt power up, there was a puddle of water beside the base of the computer, not directly underneath. I thought someone in the household has spilled a drink and wouldnt admit to that fact. When I opened up the PC, I discovered no liquids in the chassis, so I assumed no liquid got in. However the PSU did fail the paperclip test and I had it RMA'd.
After I installed the new PSU, and turned on the PC, the watercooled heatsink was making a growing loud squealing sound. I immediately powered off the PC. Trouble shooting attempts had me connecting the heatsink to its own molex connector. (I thought the sound was due to a lack of voltage).
Does this seem to add up to you guys?