You obviouzly didn't look carefully enough at the 'sticky' post called "How to use this forum - please read." Try again and pay particular attention to item #11. A photo of your setup will help as well.
Like floresta said, without much information, you can't really get a specific answer.
Though if I remember correctly, when I had that problem I think I missed to do "lcd.begin()" or I initialized the wrong display size(The example is for a 16x2 display while I have a 20x4)
It was a while since I had the problem and I don't have it connected right now so I cant test.