If the microwave does not start cooking, it's likely another program is already entered into the oven; press [Stop/Reset] to cancel the previous program and enter a new program according to the operating instructions for your model.
If the water is warm, the unit is working correctly.
If the water is still cold, check if the microwave is in Demo mode. What is Demo Mode.
Note: Not all models have demo mode.
If the Microwave is not in Demo mode contact a Panasonic Authorized Servicer for evaluation.
The food was not evenly distributed within the microwave oven cavity.
If the Microwave is still not cooking/heating evenly you would need to contact a Panasonic Authorized Servicer for evaluation.