Reinstall slack on your system. You can try to install Lilo again to the mbr, if it fails dont worry about it. After the install is done leave the install cd in the drive and reboot.
It'll want to boot from the cd again. You want to do this
I forget how it goes but it basically tells you what to type on screen. Assuming that the hardrive is hda ( dunno anything about laptops ) youd type something to the effect of
bare.i mount root=/dev/hda1 noinitrd ro
This will mount your linux system. Your lilo.conf should already be setup in /etc/lilo.conf from the slack setup.
After bootup, login as root with whatever password you setup during setup and type
$ lilo -A /dev/hda # will activate the partition you set as bootable if it needs to be
$ lilo # will make sure you dont have errors in your lilo.conf
$ lilo -M /dev/hda -mbr # will update your master boot record and actually work!
During setup in my experience doing the easy install of lilo has worked for me 1 out of 10 times if that hard drive had something else on the mbr. At first id fix it by booting up with a win disk and fdisk /mbr but then i found the above works just fine. Also the expert install of lilo ( dunno why ) seems to work a whole lot better for me to. Only failed maybe 1 out of 8 times for me thus far ( in which i did the above )