I am running Fedora 15 on VirtualBox. It runs fine until I install the guest additions pack. Once they're installed, it will boot fine but stop at a blank screen with a blinking cursor. The screen will accept text inputs, and register any special keys as text (e.g. "]^12"). I can get into grub and get into Runlevel 3. I then have no issues logging in, or navigating the file system, but I cannot start the GUI. I know that it's possible to fix, I just do not know how.