There is something in the screen but it is not visible.
I am sorry, this is too vague. (And contradictory: if it isn't visible, how do you know there's something there?)
Video issues can be a range of things, is it the video-card, the monitor itself, the x-server? How can we tell?
Generally it is a good idea to say what your video card is, what drivers you are using, and show us your /etc/X11/xorg.conf file. Your syslog files may show you something is up too. However: all this assumes you have another monitor that works?????
If so, then, most likely your xorg.conf settings are correct for you old monitor and not for the new one. eg. When I changed from a crt monitor to a lcd, in FC4, I found I had to substantially lower the refresh rate to get a picture.
However, if you never had a different monitor (then how did the graphical install go?), then it is not so easy.