I have a board with the exact same symptoms prior to failing. Keep in mind this was like 3 years ago...
I was never able to figure out what happened to the board. Swapped in new processor, new capacitor, new roms, new RAM with no success. I gave up and just bought a rottendog controller board to resolve the problem. I think it was $89.
You need to confirm +5 on the PCB (past the two pin connector) at an IC or two, in order to confirm that the voltage is getting to the IC's. I still have my board, marked as BAD but no longer can test it since I don't own any DE DMD machines any longer.
I found the THREAD where I asked for help here:
https://pinside.com/pinball/forum/topic/tftc-help-destern-whitestar-dmd-display-controller-boardrottendog-dps004