IMHO could be a 'cd-drive_related_issue' but even a 'cpu_related_issue'.
With regard a this last assumption consider that I work with 10 pcs with the same hardware. It was happened that 2 of this pcs have had a motherboard crash after 3 years from buyng. So I've replaced the old motherboard with a brand new one, most recent and more powerful with a more powerful cpu, while the cd-drive have remained the same. So I've discovered that some linux-live-cds (not knoppix) and even install-cd (slackware) doesn't load on old pcs with old motherboard (with errors messages in loading stage and even not recognized as boot device at all) but load painlessly on new motherboards with the same old cd-drives!!