I know this is old but I thought I'd comment about a similar problem I had.
My UM2 died 10 mins into a print as yours did, although I had no lights no nothing, wouldn't turn on or anything. Power brick was fine (tested with multimeter).
I had recently replaced the nozzle temperature sensor.
Turns out when I unscrewed the hot end and screwed it back up again after feeding the thermocouple wires through, I had just nipped the corners of the fan wires in between two of the aluminium pieces. I didn't realize I had done this and it didn't give me a problem until the hot end heated up thoroughly then the insulation melted and the wires shorted out.
It was simple to fix by separating the wires and re-insulating them. My UM2 is now back in business.
I thought, like you, that I would need a new board as it appeared totally dead. Very pleased it was such a simple (and stupid on my part) problem.