Check your BIOS to see that there is nothing funky there and that all your hard discs are enabled properly, then booting from the FC5 install disc and getting into linux rescue.....at the prompt type # chroot /mnt/sysimage
type # fdisk -l enter
then read through the output and you will see where each OS is:
From your previous postings I am just guessing that windows is on /dev/hda and FC5 is on /dev/hdb ?? If so, then
type # grub-install --recheck /dev/hda
enter type exit
and reboot and you should be good to go.