IPhone is not starting

1. Try and Force ReStart Your iPhone as instructed in this article by Apple ➔ How to Force ReStart your iPhone. If that does not work then -
2. Follow the instructions in this article by Apple ➔ If your iPhone is Non-Responsive or Frozen and see if that does not work then-
3.  Have your iPhone examined at the Apple Store or at an authorized service center. If the stores are closed then please contact ➔ Apple Support

Axel F.

Is, using this support guide (second paragraph) your screen doesn't come back on:--> If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

it might be a screen failure.

Regards

Giulio