without knowing anything other than whats in this post:
Is it wired right? Check the connections again, even if you KNOW they are right. Get someone else to check them (rule #1 is that the hardest mistakes to find are your own).
Did you use the right wiring diagram? Don't rely on a "this is close" diagram. The screen you have could be completely different from the schematic you are using. Again, double check.
Is your power supply good? Make sure the supply you are using provides enough voltage and amperage for your screen/backlight/whatever.