GUI.Label doesn't show on screen

I am new to Unity and working with GUI. I was able to create GUI Buttons perfectly but when I am drawing GUI Label my code doesn’t work and I am not able to view the label on screen.
Here is my code snippet -

void OnGUI()

	GUI.Label (new Rect (550, 200, 800, 100),"Choose Level"); 


What am I doing wrong or missing something here?

Is your label to big that it goes off frame? That may be the problem.