Dark screen but could see the desktop items when externally lit

While i was watching a video my screen went dark but i could hear the sounds play, when i had a closer look with a my mobile flashlight things were fine on the screen except for the light...after i tried every reset and other options nothing changed. Display comes on when the screen brightness is kept on the last two slots . On booting the startup screen is blinking...and it stabilises only at the user and password screen...where must be the problem , is it the logic board or the invertor cable...??