First make sure that the floppy has a bootable ("blessed") system folder. If it doesn't, the PB will spit it out, exactly as it's doing.

Occasionally, a damaged hard drive will cause the floppy drive to misbehave. To test this possibility, remove the hard disk altogether, then try to boot from a blessed floppy.

The fact that it chimes should give you encouragement. If it gets that far, it usually means that a little extra work will put you over the top, so don't give up!