Check the power cord and ensure it is firmly connected in the microwave and in the local power supply. If it is not connected completely, certain components on the microwave may work, but others will not.
Remove all other appliances from the same electrical circuit so that the microwave is the only appliance plugged into that particular circuit.
Unplug the microwave and unscrew the light bulb in the microwave. Replace with a new light bulb and plug the microwave back on.
Firmly close the microwave door and press "Stop/Cancel" to ensure the timer was not pressed instead of a cooking feature.
Reprogram the microwave for the desired cooking time and press "Start". The microwave should now cook properly.
Contact an authorized service technician if the above steps do not resolve the issue.