Diagnosis
That's the automatic shut-off kicking in because the styler isn't moving. It thinks it's been left on and idle, so it powers down for safety.
How to Fix It
The fix is to simulate actual use to reset it. Pick up the styler and gently rotate the barrel a few times. The motion sensor needs to detect movement. After rotating it, press the power button again. It should heat up normally. The three-beep warning is your cue to move it before it turns off.
If That Didn't Work
If it still beeps and turns off even while moving, the internal motion sensor might be faulty. Unplug it, let it cool completely for an hour, then plug it into a different wall outlet directly (not through an extension cord) and try again. A hard reset can sometimes clear a sensor glitch.
Heads Up
This 'sleep mode' feature is aggressive. You can't just leave it heating up on the counter while you do your makeup—you need to pick it up and start styling within about 30 seconds of it reaching temperature, or it will beep and turn off.