hm, if the HD is not detected in the BIOS, then you have a Problem... I guess you didn't play around with the jumpers, no?
Well, if your system doesn't detect your HD (you can also see that in the first boot screen, just hit "pause" to get more time), then Knoppix won't either.

same thing happened to a friend of mine yesterday. His Notebook broke down, completely! Doesn't even boot without the HD, so the mainboard must be broken. I took his HD out and plugged it via USB to my computer, and the HD didn't even spin! (And my BIOS didn't recognized it either). All his Data is lost...

I hope it's not the same problem you have right now, because there is no hope (or maybe a really expensive one, don't know for shure)