Diagnosis
The door isn't fully latched. The machine's door switch isn't registering as closed, so it beeps to alert you and refuses to run.
How to Fix It
Open and firmly re-close the door. Don't just push it shut; give it a solid, confident push until you hear the latch click. Check for any dishes, utensil handles, or the detergent cup obstructing the door seal. If the door seems loose or doesn't feel like it's catching, inspect the latch mechanism on the door frame for debris.
If That Didn't Work
The child lock might be accidentally activated. Press and hold the Heated Dry
Heads Up
If the door latches fine but the 3-beep error persists, the door switch itself could be faulty, which requires a service call. Don't try to bypass it.