If lilo is installed, you more than likely have one of these 3
1 - lilo pointed to wrong partition (easier to do than you think if you've more than one linux partition).
2. Plug and play turned on in the BIOS, and a conflict with the hotplug script.
3. Bad copy of the kernel on your HDD. (either wrong one, or not a perfect copy of the right one, for some reason if you see a cdrom read error at the end of the install while rebooting you 100% positive have a non-perfect copy).
I've installed Slack 7 and up on hundreds of production computers, as well as customized versions on some crazy hardware and IMO those are the most common slack install errors.