I'm not going to delete the post, but I may move it to General Support or New to Linux, it seems out of place where it is.

As to your problem, it is a strange one. The command that you used normally should have ended up getting your C parttion. So lets asks a few questions: Tell us what C and D are normally. Are they 2 partitions on the same hard drive? What types of partitions are they? Has a strange Windows problem brought you to Knoppix to try to recover C (and what are you seeing in Windows?) Could C be damaged so badly that even Knoppix can't find it and so D seems to be the first partition? Have you tried to mount hda2 and what happens when you do?

Did you do anything really nasty or stupid that may have deleted the C partition from the partition table? It might be recoverable if this happened and you take the right steps before any more harm is done, but if so admit it and tell us now.

Looking at this a different way, there normally are desktop icons on the Knoppix desktop for each hard disk partition that Knoppix can find. What does your Knoppix show when it boots? You should have 2 icons and should be able to click on them to open them in read-only mode (or right click and use the actions su-meny to make them writeable if they are not NTFS paritions).