Screen gets dark

I made a small application showing a cube one can rotate using the arrows keys.
As so - if one press the “End” key I get the depth buffer into an array and save it.
The problem is that after getting that buffer (I use the glReadPixels function) I get a black screen - so I can not get that buffer more then one time for each execution…

Hello, could u post some code ?? It should help me to see what is ur problem