Sreen won't turn on after phone was dropped but not cracked

My wife dropped her phone and afterward the screen just stayed black. Screen is not cracked and has no visible sign of external damage.

The phone is still working, the alarm still went off every day with no way to turn it off until the battery died. Tried charging, restarting but no change. Then removed the screen, detached and re-attached the screen connector but that also did not help.

Does anybody know if a screen replacement would fix it? Or is it something with the motherboard and there's no video output to the screen? I see no damage to the screen itself.

Is there a way to test what's broken without a functional screen? I know USB debugging requires a screen confirmation so can't do that:(