Diagnosis
The membrane keypad has failed or there is a fault in the control board circuitry. Power is present, but input signals are not registered.
How to Fix It
Unplug the microwave. Clean the keypad surface with a damp cloth to remove debris. If buttons remain unresponsive, the membrane keypad may need replacement. Access the control panel and disconnect the keypad ribbon cable. Replace with a new keypad.
If That Didn't Work
The control board itself may be defective. Test for power output to the keypad and consider board replacement.
Heads Up
Avoid using harsh chemicals on the control panel. They can damage the membrane and cause further issues.