i dont know about the x10 as i havnt stripped one down, people on here have though. But a laptop screen, LCD have a Seperate invertor which powers the backlight, basically its like a starter on a strip light. the new LED laptops have a Invertor Built in.
So id expect something simular with the phone.
IF the screen is working in another then it rules out a Built in Invertor being faulty, so i would say there is another cable somewhere OR the invertor in your phone is also faulty.
Good Luck