Acer Aspire 5733series running Windows 7 Home Prem.

Please help. My laptop was fully functioning until the scree randomly begun to flicker then went completey black but the back light still working. I have since followed ALL steps of elimination to dicover what the issue is, including everything from battery & ac removal to RAM & HDD checks and Motherboard and GPU testing, all of which are working fine. When connected to an external display, nothing whatsoever is displayed.
As it stands today, all hardware and components are working, windows 'sounds like' it is starting as normal and the back light is working on the screen, but still nothing at all is displayed.