Fully functional computer, dead screen.

So my mother gave me her old 2009 17” MacBook Pro. She had recently gone on a trip and a water bottle leaked in her bag and got the hinge edge of the computer wet. After that the screen was dead. The computer still works perfectly when hooked up to an external monitor.

So my question is whether or not it’s definatley the screen that’s dead or something else? And how can I determine that? I’m worried that if I buy the replacement screen and take the time to instal it, it could be something else that’s gone bad. Thank you.

I can see a faint image when the light is shown through. When I opened it up before I cleaned off the connectors on the monitor cable as best I could. I can open it up again later and take pictures.