Try going onto a command line in maintenance mode (or repair mode, or single user) and running the following as root (or preceded by sudo):
If that doesn't work, use nano to alter the menu list to remove the splash option.
nano is a command line editor. To exit from the file and save your work, press "Ctrl-X", at which point it'll ask if you want to save the file, which you would.
There's usually something like the following:
kernel /boot/vmlinuz-2.6.26-1-686 root=/dev/hda1 ro splash=silent
Your menu.lst will likely say something different for splash. Regardless, just try eliminating the splash option, and see if you have any luck. Or maybe even simpler is to remove the package usplash via "aptitude remove usplash"
Maybe if you try the command "startx" at the prompt, something will happen.
disclaimer: I use Debian, not Ubuntu. So, my advice may not apply. For that matter, given that I'm a pretty average guy, even if you were using Debian, my advice may still not apply.