Thanks for your reply! The issue is half solved:
Now Debian works again, but I had to install knotix in the slackware partition
Now with the knotix intall I changed from lilo to grub and added debian booting options into the menu.lst of grub and now everithing works fine.
I´m going wait a bit untill my next try with slackware, I need debian working for my class works, but in a few weeks maybe...