screen is full black

The LCD layer of the screen is most likely cracked which will result in no image being displayed on the screen. You will most likely need a new screen to resolve the issue. You can also always check the connection from the screen to the board as in some rare cases the flex cable can become slightly disconnected. Liquid damage can also cause this symptom. Just mentioning in case the device was near liquid recently.

If your screen is completely black but you can still receive calls, there are a few troubleshooting steps you can try:

• Restart Your Device: Sometimes, a simple restart can resolve many software-related issues. Press and hold the power button until you see the option to restart, then try turning your device back on.
• Check Screen Brightness: It's possible that your screen brightness is turned all the way down. Try adjusting the brightness by swiping down from the top of the screen (or up from the bottom, depending on your device) to access the quick settings menu.
• Perform a Forced Restart: If your device is unresponsive to regular restart attempts, try a forced restart. The method varies depending on your device model, so you may need to look up specific instructions for your device.
• Check for Software Updates: Make sure your device's operating system is up to date. Sometimes, software bugs can cause issues like a black screen.
• Charge Your Device: If your device's battery is critically low, it may not power on properly. Plug it into a charger and wait for a few minutes before attempting to turn it on again.
• Boot into Safe Mode: Booting your device into safe mode can help determine if the issue is caused by a third-party app. If your screen works in safe mode, try uninstalling recently installed apps or performing a factory reset.
• Factory Reset: This should be your last resort, as it will erase all data on your device. Perform a factory reset only if none of the above steps work and you're willing to start fresh with your device.

If none of these solutions resolve the issue, it's possible that there's a hardware problem with your device's screen