My guess is that you did not burn the image properly. This topic is explained extensively in the forums. Basically if you burned your cd by going into your burning program and selected the knoppix.iso, then you have the iso burned to the disk. Buring an iso to the disk is not the same as making a bootable disk from the iso. Many of the cd burning suites out there have documentation. Look up burning from an image. If you know how to burn images and you know you burnt it properly you will want to check the md5sum of the file to make sure it is ok.