If your iPhone, iPad, or iPod touch won‘t turn on or is frozen, see if the things in this support article resolve the issue --> If your iPhone won't turn on or is frozen - Apple Support
You may have to get Apple to have a look at it:
Go to this page to find your nearest Apple Authorized Service Provider (AASP) or Apple Authorized Distributor (AAD) --> Find Locations
How to make a Genius Bar appointment
1. Go to Genius Bar Reservation and Apple Support Options - Apple
2. Go to "Get hardware help".
3. Select your hardware and continue selecting options requiring replacing parts until you see "Bring in for Repair"
4. Sign in with your Apple ID