Diagnosis
The power supply is interrupted. The most likely cause is a tripped thermal fuse in the plug or a loose connection at the unit's inlet.
How to Fix It
Unplug the unit. Check the power cord plug. The Ninja SL400 plug has a built-in thermal fuse and reset button. Press the red reset button on the plug firmly. Plug it directly into a wall outlet, not a power strip. The display should light up.
If That Didn't Work
Inspect the power inlet on the back of the air fryer base. Ensure the cord is fully inserted and the pins are not bent. Try a different wall outlet. If still dead, the internal main board or thermal cut-off is faulty. This requires service.
Heads Up
Never bypass the reset plug or use a different cord. That safety device prevents overheating. If the internal fuse is blown, it's often due to a failed heating element or fan motor.