This sounds like it may be a blown fuse. There are three removable fuses on your RAMBo board:
F4: Automotive-style 15AMP ATO fuse - supplies heated bed F3: Surface mount NANO2 fuse - supplies logic, heat, and fans F2: Surface mount NANO2 fuse - supplies motors
You can check if the F3 fuse is the root of this issue by switching it and the F2 fuses position on the RAMBo. To do this first make sure the power button is in the OFF position, and then disconnect the power cord from the printer.
Next remove the side panel of the TAZ 6 control box so we can get to the RAMBo board, there are 14x 2mm allen head screws along the edges of the side panel. Take steps to ground yourself while working on the board to avoid shocking it.
The F3 fuse is what we suspect is blown, because it supplies logic for the machine. We’re going to swap it with the identical F2 fuse, which corresponds to the motors. First remove the F3 and F2 fuses, tweezers work well for removing these fuses from their tan colored mounts. Make sure to pay attention to which fuse is which. With the F2 fuse now in the F3 slot, and vice versa, please close the control box and plug the printer back in.
Attempt to turn the printer on, and if the printer turns on and the LCD display responds, we know the RAMBo is in working order. Keep in mind you will not be able to use the printer in this state, as your motors fuse is now the “bad” fuse.
If this indicates that the fuse was the issue, then replacements can be purchased here: