When you get to the white screen hit 'ctrl+alt+backspace'. This should get you to a command line prompt.
- make a backup of the xorg.conf found on your hard drive
- overwrite the xorg.conf on your hard drive with the xorg.conf on the live cd
- remove the live cd and reboot
If that doesn't work, restore the backup xorg.conf and ask on the debian mailing list. If THAT doesn't work, install PC-BSD.