DIAGNOSIS The microwave is throwing an error state. The three-beep sequence indicates a control panel or touchpad malfunction.
FIX Unplug the microwave for a full five minutes. This resets the control board. Plug it back in. Press the Stop/Clear button twice. Then attempt to enter a cook time again using the number pad.
IF THAT DIDN'T WORK The membrane touchpad may have a failed section. Clean the entire control panel with a slightly damp cloth, then dry thoroughly. Press each button firmly and deliberately. The issue is often with the Start or numeric '0'/'1'/'2' buttons.
HEADS UP Do not press buttons rapidly or before the display fully initializes after plugging in. This can retrigger the error.