iPhone 15 Pro won't turn on after charging

Turn on iPhone

Press and hold the side button until the Apple logo appears.

from:

Turn iPhone on or off - Apple Support

if no joy, be sure it was really OFF.

Volume-Up, Volume-down, hold side button for a half minute

if still no joy:

Official Apple Support

Chichita48 wrote:

I left my iPhone 15pro charging and in the morning was off. I was not able to turn it on. I tried volume up and down and power button but it doesn’t work. Help.

For the last step of the Force Restart, how long did you hold the side power button? You may need to KEEP HOLDING it for up to 30 seconds or more. DON'T let go of it until you see the Apple Logo. Try again. Volume Up, then Volume Down, then hold the side power button and KEEP HOLDING it.