Iphone SE shutdown screen

Connect to a computer and do a restore via iTunes after backing up your phone.

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

If that does not fix the problem, make an appointment at the Genius Bar or at an authorized service provider to have the phone evaluated.

RodolfoB wrote: "iPhone SE, iOS 11.2"

Rodolfo ~ Are you sure you're running iOS 11.2 or later? (Check via Settings > General > About > Version.) ...And see this Apple Support Article:

If your iPhone, iPad, or iPod touch unexpectedly restarts

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Hello RodolfoB,

If you believe you're having hardware issues (from the sounds of it, that seems to be the case), I'd recommend setting up a repair for the device at http://apple.com/retail with your local Apple store. If that's not an option to you, contact AppleCare so they are able to do a mail repair for you.