I'm not sure if this makes sense, but when I had problems with the graphical mode not starting, I ran xorgconfig as root.
Type "su", then the root password, then "xorgconfig".
This nice utility will ask you questions about your graphic card, keyboard, mouse, and monitor (more or less the same ones that were asked during the install but a bit more specific. It's handy if you have your monitor's manual at hand to set the Horiz. and Vert. frequency options.
After that the problem was solved for me.