While you're waiting for someone smarter to reply, test the CD from which you installed Knoppix to see whether it's corrupted, which could certainly give you the problems you describe. Just boot the CD with the argument "knoppix testcd" and watch the screen for a couple of minutes (the results of the CD test only remain on-screen for a few seconds before the boot routine proceeds). (Thanks, forum, for teaching me this a few days ago!)

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