When I boot with a disk insert then sda1 - sda4 appears on the desktop. And it does not work!

Do you have a HD Installation?

Try to boot from cd without inserting a disk and then modify the fstab file like above for the correct filesystems, vfat (dos) in most cases.

Create LS120 Icon then.
In the Icon settings for the LS120 disk you must entry sda.