This usually occurs after the power cable is over-extended. It usually requires a simple reset.
To reset the sit/stand functionality, lower the desk fully using the controller on the right. Wait 10 seconds and then hold the down button for about 5 seconds or until you hear clicking and/or feel the desk “bounce” lowering and rising on its own. Press the button up, rising the unit to a comfortable height. If it is still not responding, repeat the procedure allowing about 30 seconds between.