I believe ddc has to do with features of plug and paly. There are threads on this through google.
But before we assume the worst how does windows see you monitor? Is it recognizing it the same
as it did?
Also here:http://www.knoppix.nl/3.6/knoppix-cheatcodes.txt are the specific cheatcodes for 3.6 you could try to load the nv driver at boot.
knoppix xmodule=nv|radeon|savage|s3 but I don't know if that will fix your problem.

If you can see the screen enough to use it you might try to configure the xserver.
Have your monitor specs and do "dpkg-reconfigure -plow xserver-xfree86"

Good luck