What happens if you don't enter anything? Knoppix should pop right up in default configuration. There's a point in boot-up where it hesitates and offers you the opportunity to enter some flags (also called "cheat codes") for booting in some specialized fashion. Not knowing specifically what it said or what you entered, I suspect that you inadvertently requested some specialized function that your computer, as presently configured, doesn't support.

Just pop the CD in and toggle the power, and stick your hands in your pockets for 2-3 minutes, and see what happens.

JD