We cant just tell you what to do to fix it because we need to know specifically what is wrong. Is is the display, the display cable, is it the circuitry on the display, is the display circuitry on the logic board, etc? You will need to determine what is wrong first. If it were me I'd be looking at the cable from the display to the logic board and ensure its plugged into its respective connectors properly and there is no other damage. Also while in there tighten up the hinges. If that doesn't help then you will likely need to get another display to see if it works. if it works then the display installed died. etc. Perhaps reach out to the people that did the repair...