After replaced the display unlock screen got fully black

The ribbon on the display of the phone was broken and a new display was installed. Worked fine for a few weeks and then when locking and unlocking the phone screen it appears dark. After unlocking the lock two or three times, the display appeared. Tried flashing the firmware again and same. If I want to get the screen again, press the power button and restart the phone. What error is this? On the phone or on the display?