Latitude 7440 Power button not working

It was good the night before, but now I am not able to start the laptop. I tried to download pictures from my old iphone yesterday, not sure if that could cause this problem.

The power button has light flashing every 3 seconds with a static sound. Screen is dark all the time.

I tried following steps but no luck:

1. Disconnect the power adapter

2. Disconnect the laptop battery

3. Hold and press the power button for 20 seconds

4. Reassemble all peripheral but still no luck.

My battery is fully charged but still no luck, please help.

 

Thank you!