First check if you can see if there is anything showing on the screen, by shining a light (torch) on it at an angle. If you can see the desktop for instance then the backlighting is not working. This may be due to a faulty inverter or and I'm not sure about your model, but some have a magnetic lid switch (usually mounted at the base of the screen either in the left or right side - magnet in lid switch in body but sometimes reversed) that turns off the screen when the lid is closed which may be faulty.
Can you get the screen to even flicker by pressing near either hinge, as this is usually where the lcd cable passes nearby to get from the case to the lid, in case it is fractured?
It may well be a loose video flex cable connection either at the screen end or on the motherboard. Here is a link which shows the dis-assembly of a N73 series laptop.
https://www.youtube.com/watch?v=NXSoMqb6.... This may be of some assistance in opening the laptop
If it is none of the above it is then either a faulty screen, faulty video flex cable or it could be a faulty motherboard, as this is where the power comes from for the backlighting.
Hopefully this is of some help.