Make sure that the computer isn’t trying to boot off of a CD Rom/DVD that isn’t a bootable disk (ie. remove any disk from the drive). If that doesn’t do the trick get your install disk for Windows 2000/XP/Vista (which ever you are running) and put it in. Boot off the disk and go through the repair option and see if it can repair the installation and fix the boot problem. If it can’t, as a last resort you may need to reinstall Windows.
Try this solution.
Try to disable floppy A in CMOS.