Far from expert here, but you might just be having trouble with booting into a GUI login. I personally never boot to a graphical login until I have done all the tweaking I need to do; I always manually start the GUI after logging in until I'm happy with everything.
One "default" window manager had me fooled into thinking my Xwindows configuration had frozen my system until I accidentally did a right-mouse-click during some troubleshooting. If you are booting directly into a similar window manager, it could mimic the symptoms you describe. To check, do a right-mouse-click on the black screen and see if a menu pops up; if so, then you just have the infamous basic window manager black window.
You should be able to use your install CD to do a "rescue" type boot from the CD and edit the files on your hard drive to change your boot runlevel so that you boot to a command line. Never have done Fedora myself (I'm a Gentoo fan), but this page has a grub edit for Fedora that might help you: