blank screen, video out works on another monitor

My screen is blank/black but does light up. When I plug another monitor in it the system works fine. I read about a led test but it appears that it may be for previous revision, I do not see any leds. Since the video works on another monitor and the screen lights up (means inverter is working) would this mean it is the lcd that has failed? Are there any other tests I can do to determine the issue?

To clarify, the lcd does light up all the time. When using the system from the external monitor I can change the brightness of the primary lcd and see it respond accordingly, so i think the inverter is working properly.

I did re-seat the video cable and the inverter cable at the logic board anyways, no change. I am running a diagnostic from techtools dvd and on the basic test everything passed. (using external monitor) Ran the advanced test which does all the basic tests plus checks hdd and file system etc. After it had been running about an hour to and hour and a half the screen came on!!! I am now not sure what the issue is. It looks normal so I know the physical lcd is working and inverter is probably fine to. the only thing i can think of is after it is on for awhile and heats up a proper connection is made somewhere. I guess it could be the video connector possibly, i did wiggle it without any affect previously. I did reset smu and pram when I had it open as well with no apparent change. Any ideas what is going on?