Go into the bios and change the boot order so that it looks at the hard drive before the floppy. If the hard disk is faulty or corrupted you will get something like "invalid system disk" and be prompted to insert a valid disk. You can create a boot floppy from a working computer and use that to boot up. If the machine in question has a cdrom drive, be sure to include cdrom support on the boot floppy. I always advise people to write protect their boot floppy after creation. That will prevent any virus that might be lurking on the hard disk from corrupting the floppy.
