When an MGC Pro Board is fully functional but not showing anything on the screen, then likely the contrast is turned down not allowing anything to show.
In order to correct this, a power cycle of the MGC Pro board must be done, and while the screen is rebooting (within the first 5s of restoring power), a few toggles of the "UP" arrow must be done repeatedly until the screen starts to display again.
Here is the portion of the MGC Pro Board Manual that explains how to adjust the contrast: