This is a common problem to almost all those who are starting to work with lcd. If it is showing black box in first row , then most probably the Lcd is good. If it is initialized properly then only it enter to working mode. At this time the black box disappears... In your case, i think for 99% the LCD is good. And also, I hope it is initialized.
Do one thing,
Just remove the microcontroller. Then switch on the power. Now observe the LCD. If it shows black box as earlier, then you can almost confirm the LCD is good.