Found this on another forum:
here is a a breakdown of screen issues.
Vertical Lines - Bad LCD or LED Screen
Dim Screen - Bad Inverter, Backlight, or (unlikely) Motherboard
Garbage On Screen (symbols) - Bad Video Card
Horizontal Lines - Bad LCD or LED Screen or Video Card
White Screen - Video Cable not connected, but inverter cable is still connected
Black Screen (No signal) - Video cable (Motherboard Side) not connected or (unlikely) both video and inverter cable not connected
Partial Black Screen - Bad Screen or Video Card