Korg Triton Touchscreen - blue flash

I have a Korg Triton Pro that I am repairing. At power on, the touchscreen will flash blue, and then go black, and not work. With a working KLM 2091 power inverter board, and a working touchscreen, the problem still persists - a black, non working touchscreen. Other red lights work, and the screen will beep when touched. What causes this problem???