iPhone X won't power up

I think you already know what Plan B might be.

There is a hardware problem with the phone that will need attention at the Apple Store (make an appointment) or take the phone to an authorized Apple Service shop.

You can find a list of authorized service shops in your area using the link just below:

Find Locations

Might be something as simple as a defective battery.

See this, but if it doesn't work, your Plan B will be a visit to your Apple Store Genius Bar for evaluation and options --> If your iPhone is stuck on the Apple logo - Apple Support