I'm brand new to linux, so please go easy on me.

I've burnt knoppix to cd and manage to boot from it on one of my PCs.
It boots up and when it says "press enter to load LiveCD" I press enter. Then after a second or so it says something like:
"You passed an undefined mode number"
"Press <enter> to see video modes or press space to continue"
I press space and then it proceeds to load Knoppix.
After a while it says "Loading X Windows" and then my screen just goes black and nothing happens.

Please can you explain how to fix this!

Thanks a lot,
raZer