If you are using a floppy to boot Linux, you may need to specify the location of your Linux root partition at boot time. This is especially true if you are using the original installation floppy itself, and not a custom boot floppy created during installation.
While booting the floppy, hold down or . This should present you with a boot menu; press to see a list of available options. For example, many distributions allow you to type
boot: linux hd=
at the boot menu, where is the name of the Linux root partition, such as /dev/hda2. Consult the documentation for your distribution for details.