Diagnosis
The three-beep alert is the opener's 'travel limit error'. The logic board thinks the door is stuck or has hit an obstruction during its last cycle.
How to Fix It
Manually disconnect the opener from the door. Pull the red emergency release cord down firmly. Operate the door by hand to check for binding or an actual obstruction. Clear it. Reconnect the opener by lifting the door about halfway and pulling the release handle toward the door until it clicks. Press and hold the wall button until the opener beeps once. The limits are now reset.
If That Didn't Work
The safety reversal sensors may be misaligned. Check the yellow LED lights on both sensor units. If one is blinking or off, realign them so both show a steady light. Clear any spider webs or debris from the lenses.
Heads Up
After a power outage, the opener defaults to this error state until you manually reset it. It's a safety feature, not a failure.