Diagnosis
Three beeps indicates an invalid command or a door interlock issue. The control system did not receive a valid start signal.
How to Fix It
This is often a sequence error. Ensure you have entered a cook time or selected a sensor cook option before pressing Start. If you have, the door is likely not fully closed. Open the door and firmly close it again until you hear a definitive click. Listen for the click. Then re-enter your time and press Start.
If That Didn't Work
If the door seems loose or doesn't latch firmly, inspect the door latch hooks and the corresponding slots on the microwave frame. Look for obstructions or damage. A misaligned door will prevent the safety interlock switches from engaging.
Heads Up
Do not try to bypass the door switches. The three-beep error is a safety feature. If the door latch is physically damaged, the unit must be serviced to maintain its radiation seal.