First, type typing knoppix xmodule=vesa at the Knoppix boot pompt.

If that doesn't help, try typing failsafe at the boot prompt. You will not like failsafe mode, networking and some other stuff will not work, your mouse might not even be detected, but if knoppix comes up with a KDE gui screen that will tell us a lot and you can work on figuring out what cheat codes that you need from there. Hit F2 and/or F3 at the boot prompt for more details.