The floppy drive was probably disabled in the BIOS. To change the setting, you need to watch your POST screen when you first turn on the PC. Usually, it'll tell you which key to hit to enter setup: F1, F2, ESC, or Delete.
Once your in, look for and change the boot order. Select the floppy as the first boot device. You'll want to use a Win98 boot disk in order to get a DOS command prompt.