Ok, looking at manuals led21 is 5v power, so that's good.
led19 should light for a second then led 20 takes over and flashes continuously indicating the CPU is running.
Not sure what's causing the issues, but it seems the CPU isn't running, I would hold fire getting a new DMD if I was you, I'm not convinced the cpu board is getting far enough to actually send it any data to display.
This is where stuff gets a bit beyond me, but I would try reseating all the roms on the board and give the asic chip a gentle push to make sure its seated all the way.