So I pulled the ribbon cables out of my JM to test something on another machine. Then I reinstalled cables.
Flipped the machine on. The DMD filled it's pixels with lights, the machine buzzed... and then: NOTHING. dead.
I took the backglass off... flipped the power on again... no signs of booting up. No lights...
I did a quick check of the fuses, they all seem to be fine.
This depressed dude needs a little hand holding.