Here are a few troubleshooting steps you can try to resolve the problem:
1. Force Restart: Press and hold the Power button and Volume Up button simultaneously for about 10 seconds until the device restarts. This can help refresh the system and resolve minor software glitches.
2. Check Display Settings: Make sure the brightness level is not set to the lowest setting. You can adjust the brightness by going to Settings > Display > Brightness.
3. Charge the Device: If the battery is critically low, it may cause the screen to appear black. Connect your device to a charger and let it charge for at least 15 minutes before attempting to turn it on again.
4. Boot into Safe Mode: Restart your device and when the HTC logo appears, press and hold the Volume Down button until the device finishes restarting. This will boot your phone into Safe Mode, where only pre-installed apps are allowed to run. If the screen works fine in Safe Mode, a third-party app may be causing the issue. You can uninstall recently installed apps to identify the culprit.
5. Factory Reset: If none of the above steps resolve the issue, you can try performing a factory reset. Keep in mind that this will erase all data on your device, so it's important to back up your important files before proceeding. To factory reset, go to Settings > System > Reset > Factory data reset.
If the problem persists even after trying these steps, it may indicate a hardware issue. In that case, I would recommend contacting HTC customer support or visiting an authorized service center for further assistance.