First.. please keep posts to just one forum, so replies can all be together.
Second, try booting from one of the many livecds out there, mounting hddN, chrooting into your slackware root, and re-running "lilo" to make sure the changes are done properly. Also, lilo should be set to install to the master boot record (it is most reliable this way, obviously there are other choices.) Also, why is hdd your boot drive? Multi-booting?