What other things have you tried when your iPhone only shows the black screen and won’t turn on?

You may try some of these steps, please check after each step...

1. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
2. Follow the Apple article to resolve the issue --> If your iPhone, iPad, or iPod touch won't turn on or is frozen ...
3. If not resolved; please follow the steps in the following link for support with this issue: If your iOS device restarts or displays the Apple logo or a spinning gear unexpectedly
   1. You still see a black screen after charging, force restarting, following the steps in this article.
   2. You see a black screen, but you can hear alerts, sounds, and vibrations.
   3. The screen remains black, but the device chirps when you unmute it and connect it to power.
   4. Your screen is on, but it doesn't respond when you tap, slide, or try other gestures. 
   5. You can't force your device to restart because a button is broken or stuck.
   6. Your device is stuck on the Apple logo, displays a solid color, or isn't recognized in iTunes.
4. You can put your iOS device in recovery mode, then restore it using your computer. ---> If you can't update or restore your iPhone or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.