I have HD on one IDE channel
and DVD-rom drive and CD-ROM drive on other IDE Channel (Secondary IDE)

The DVD drive was Master and the CD drive slave, and the Knoppix CD was not running OK on the DVD drive. So I switched the master and slave on Secondary IDE. The CD drive became the master (and the Knoppix CD runs OK on it) and the DVD drive the slave.


Normally knoppix will only ever open NTFS volumes in read-only, so it seems unlikely it caused your problem...
I'm pretty sure (like 99.9999999%) it was Knoppix that caused this problem.
This PC has been running for years without problems, why on earth would exactly give me this problem on the day that i run the Knoppix CD on it ???