Changing the ac dc plug on back of keyboard

No power can be caused by a number of things.

The AC and/or DC plug would not be on the top of my list unless it shows obvious physical damage.

Start by verifying you have power at your connectors.

Then it is time to open it up and trace the power. Start at the power connector, then the on/off switch, then the PCB, then it is circuit trace time. Primary cause would be diodes. You can trace power on the PCB or measure diodes with the power off.