Screen issue E6400 Latitude. Screen has power (backlight works) but no image.

Hi, I recently resurrected an old-ish Latitude Laptop E6400. It was working beautifully until yesterday. It will boot to windows, but with no image on the screen. It appears to have power, the backlight can be adjusted up and down. It works perfectly when plugged into an external monitor / TV. I wondered if this is a full screen replace or maybe a different component that needs repair. I am only slightly hardware savvy, but would welcome advice from any of you learned folk if you have any ideas / had similar issues, or guidance as to where the best place to get it fixed might be. Thanks in advance, Jason