There are a few potential causes for a black screen on a CITYCALL I8550, and several potential solutions you can try. Here are some things to try:
Restart your phone: This is often the simplest and quickest solution for a black screen issue. Press and hold the power button until the device turns off, then turn it back on again.
Charge your phone: If the battery is completely drained, the screen may appear black even when the phone is turned on. Charge your phone for at least 30 minutes before trying to turn it on again.
Check for software updates: Outdated software can sometimes cause display issues. Check for updates and install any available updates to see if that fixes the problem.
Check for physical damage: If the screen is physically damaged, it may appear black. This could be due to a crack in the screen, water damage, or other types of damage. If you suspect physical damage is the cause, you may need to get the screen repaired or replaced.
If none of these solutions work, it may be a hardware issue that requires professional repair. In this case, it's best to contact the manufacturer or a professional repair service for assistance.