After changeing 2 screens still black screen. Any ideas?

Hi.so my mate 20 pro had a damaged screen.i change one from water dammaged huawei and it doesnt worked…ok i say maybe is the damaged screen but bought new one in official Huawei store and still the same black screen but i hear charging and all starting noises and green light wen is charged. Can be damaged flexy board? Any ideas? Thanks!!!