Well that sucks. You are so close!
Have you checked to ensure that power is being fed to the monitor?
Check also to ensure it is the right polarity.
It is possible you have blown a fuse. Look CAREFULLY on the monitor board to see if one is blown.
Is this the first time you have used the screen with the carputer? If so, take the screen back to the last computer you used to test it. It might be that the car PC is not outputting the signal properly.
Give us more detail on what's up with the screen. Does it flicker/come on, LED glow, etc? Give us details on how you are powering the screen and what kind of car PC you are using.