Being the owner, you should know if your phone has some physical or liquid damage. If it does, then there’s no point in troubleshooting as that’s probably the reason why it’s stuck on the black screen. But if this problem occurred without apparent reason or cause, then here’s what you need to do:

1. Perform the Forced Restart

   The forced restart must be the first thing that you need to do when you’re troubleshooting a phone with a black screen issue. It’s a simulated battery removal that refreshes your hone’s memory and reload all its apps and services.Most often, this is the only thing you need to do to fix a problem like this, and here’s how it’s done: Press and hold the volume down button and the power key for 10 seconds. This would be enough to trigger the phone to boot up. When the logo shows on the screen, release both keys and just wait for the phone to boot up completely. If this is just a minor issue, your Galaxy S20 should be able to complete the boot process. But aside from that, this procedure will also tell you if your phone is still capable of turning on. So even if it cannot boot up completely, as long as you saw the logo on the screen, it means that its hardware is still working properly. If the first try failed to fix the issue, then try doing the same procedure a few more times and if still the same, try the next procedure.

2. Charge and force restart your phone

   You only have to do this procedure if your S20 did not respond with the first solution. It is possible that the battery is drained or there’s not enough power left to even make the screen flicker. It is also possible that the firmware crashed before the battery was drained. So, here’s what you need to do to rule it out: Plug the power adapter to a working wall outlet. Using the original cable, connect your Galaxy S20 to its charger. Regardless of whether the phone shows the charging sign or not, leave it connected to its charger for at least 10 minutes. After such time, press and hold the volume down and the power key while the phone is still charging. If the logo shows, release both keys and wait until the device has finished rebooting.