You have made a worng connection. Just see the back sibe of LCD and conform which pin is no1. and so on. Then connect it. I myself suffered from this problem.I’m giving you the pin configration of LCD you connect it as per your requirment.
1.GND
2.VDD(5V or 3V)
3.V0(Contrast adjustment)
4.RS
5.R/W
6.EN
7.DB0
8.DB1
:
:
:
14.DB7
15.LED+(~ 4.2V)
16.LED-(GND)
Just see the backside of lcd and make sure your connection is right or not.