How did you "make system backup" and "restored backup"?
What was the output when you ran "/sbin/lilo"?
The command "fdisk /MBR" is for Windows, to be run in DOS mode, not for Slackware. If you ran it, that would most likely wipe out your LiLO.
Do you know where your / (root) filesystem in Slackware is located?
If you do, put the Slackware CD1 in your drive, and at the boot prompt enter "bare.i root=/dev/hda1 noninitrd ro" and boot into Slackware. Then login as root, issue "lilo" as root and reboot without the CD. All should be well.
NB: You must substitute your / (root) Slackware partition for hda1 -- if you don't know what it is, you can keep trying starting with hda1, then hda2, etc. and it will boot when you finally select the correct one.
This
hit from a Google <Linux> search sounds just like your problem. But you can restore your LiLO with the method I gave you, rather than using a Knoppix CD as in the example.