Dead Cube saga continues...

[Tom Davidson]

Sounds like you have a worst case DC-DC failure...
When it blew, it took everything else in the cube with it.
Apple's design has no protection for overload and when the
board fails, it shorts the 28V brick supply to 5V or 3.3V,
blowing out everything hooked up to those supplies.

Realistically, you should have scrapped that machine and started
over with a new system. You cant re-use any electronics from your
original machine.