Good morning / afternoon

DVD Knoppix 6.7.1 NOT Available after RE_installing Grub

My situation in 11 steps with a Laptops

I- PREVIOUSLY on my HDD with Windows Bootloader written by the last installed
MS-Windows_OS:
1°) 2 bootable MS_WINDOWS partitions (hda1 and hda3 )
2°) Some other FAT_32 partitions.
3°) 1 partition (hda6) KAELLA 3.2 (French adapted translation of KNOPPIX 5.1.1*)
accessible ONLY via device fd0 (disk 1"44 Mo)... when I am NOT TOO LAZY to
Plug an USB drive FD !!!! ....

II- MARVELLOUS MIRACLE:
4°) I Discover the Miraculous (DVD_Knoppix_6.7.1) CHEATCODE "GRUB" on
Booting!
5°) I Become ABLE to access ALL my Bootable Partitions:
a)- hda1 (and hda3) via the OLD GRUB installed by KAELLA KNOPPIX
b)- And My KAELLA ....WITHOUT using fd0 (1"44 Mo) !!!!

III-ACCIDENT (uncomprehensible...)
6°) I try ro repaire the "WINDOWS boot" via the original CD with NO SUCCESS.
7°) "GRUB" ...becomes UNAVAILABLE !
8°) Also even the DVD 6.7.1 itself !!!!......PANIC!!!!
9°) I Re_Install "the Kaella GRUB.
10) All Hd Partitions become Accessible..Good!
11) But NEVER the DVD 7.1 and This is my REAL Problem:
a)- I always need the DVD for the programms and maintenance eventually.
b)- I CANNOT iNSTALL 6.7.1 on my HDD after TESTING.

This my 1st POST, maybe I have been TOO LONG,and / or unprecise.
I am sorry and know very few, almost nothing about KNOPPIX_OS.
I am looking for BOOKS.

Thanks you and please note the 11-b (III) (6.7.1 still not installed on HDD).