DIAGNOSIS This is almost always a power supply issue. The desk isn't getting electricity to the brain (the control box).
FIX Let's trace the power step by step. 1) Check that the power cable is firmly plugged into both the wall outlet and the black control box under the desk. 2) Follow the thick cable from the control box to the motor columns—make sure those large circular connectors are pushed in all the way and clicked into place. They can feel seated but not be fully connected. 3) The most common culprit is the small, rectangular 4-pin connector that goes from the control box to the keypad. Find it, unplug it, check for any bent pins, and plug it back in firmly. That connection powers the keypad lights.
IF THAT DIDN'T WORK You might have a dead control box or keypad from the factory. Try a different wall outlet with a known-good device (like a lamp) to rule out a tripped circuit breaker or bad outlet. If power is confirmed, you'll need to contact FlexiSpot support for a replacement control box or keypad.
HEADS UP Never open the sealed control box yourself. It contains capacitors that can hold a dangerous charge even when unplugged. If it's faulty, let the company replace the whole unit under warranty.