So, I've finally managed to open that box of magic smoke (no smoke has been seen to escape). From the first look, I see nothing wrong. Smell test was ok, there wasn't any blown or inflated caps. When you power it up, the soft button works and you can hear the relay click inside and the fan turns on (i didn't hear it before ?!? it's really quiet). The buttons on the front panel light up and stay that way. They don't react to presses. The first thing I did when I opened it up was measured the outputs on the power supply. They have little labels with voltage next to header and the power supply did provide all the voltages. I don't have a scope, so I can't check the noise/ripple.
The mainboard is nothing special.
I still think it's a bricked firmware or boot problem.