Yesterday nigth I activated my Max. Wowwww what a feeling

So all my work was right the cables and the electrical stuff seams to be right.
I followed ecxactely step by step the instruction to animate the controller with the firmware, everything runs well and the firmware was perfectly transmitted, I could see that with repetier host, because I could activate every part of the machine , BUT
Unfortunately the LCD Display doesnt show me any information, I just still see the blue light and the violet/gray blocks on the display, nothing more.
I transmitted the firmware 3 times, but the result was always the same.
So I thought that I have connected the plugs wrong to the display and the Rambo, but , no they are perfect, like the pictures in the instruction.
So what is the problem ?
Is there a pin discription, where I can see the function of every pin ? This evening I will control the soldering points but I think they are right, anyway, maybe you can tell me which pins are important for the informations ?
Thank you in advance, Christoph.