Try to print separately CMYK at 50% coverage. If there is no color on pages it could be from the ROS (laser) shutter mechanism: the shutter is controlled by a solenoid or motor and the shutter motor gears are jammed with the shutters closed.
So it will be better to have a tech.
My phaser 7750 isn't printing. All pages come out blank. Even test prints and configuration prints are blank. Nay suggestions.