Your diskette can have defects, the floppy drive can be defect, the
floppy drive cable can be loose or connected wrong or the drive could be
not configured or wrong configured in Bios or Windows.
Check the configuration and hardware.
Try the floppy, drive and cable on another computer.
Besides all this, many users have a problem with the floppy drive in
Windows XP, the cause of this is not known yet.