Apple is using a new method on how you forcibly restart an iPhone X, iPhone 8 and iPhone 8 Plus. If your new iPhone is not responsive or dead, this is how you force start the device:
Step 1: press the Volume Up button, and then release.
Step 2: press the Volume Down button, and then release.
Step 3: press and hold the side Power button until you see the Apple logo appears. It might takes a while.
You must perform the steps in sequence in order for it to work.