hello I’m John it sounds like the CCFL findly went out completely. take a flash light and put it up to the screen and see if you can make out an image on the screen. if so that is the problem. In your situation i would replace the screen do to the fact that the ccfl are build into the screens already it would just save you a headache to just replace the screen. ive attached a link of a good replacement information. https://www.laptopscreen.com/English/model/Toshiba/SATELLITE%20P55W-C5316/