I have two linux,one is FC4,another is Debian.
FC4 installed on the first HardDisk,and Debian installed on the Second HD
I boot from the First Drive,and each HD have a grub installed.
but question came,when I use FC4'grub,I can't boot Debian,the Debian can start,but in the half time it halt( still in boot process this time...),the only thing i can do now is reboot. but when I boot from the 2nd HD,Debian works well, why???

the second situation is when I boot from the 2nd HD(Debian'Grub),It can boot Debian,FC4,FreeBSD,but can't Windows.I am so puzzle with these problem,so please solve the problem for me ,thanks!!!!

the following is the menu.list of two GRUB:
FC4:
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You do not have a /boot partition. This means that
# all kernel and initrd paths are relative to /, eg.
# root (hd0,1)
# kernel /boot/vmlinuz-version ro root=/dev/sda2
# initrd /boot/initrd-version.img
#boot=/dev/sda
default=1
timeout=5
splashimage=(hd0,1)/boot/grub/splash.xpm.gz
hiddenmenu
title Fedora Core 4 (2.6.11-1.1369_FC4)
root (hd0,1)
kernel /boot/vmlinuz-2.6.11-1.1369_FC4 ro root=LABEL=/12 rhgb quiet
initrd /boot/initrd-2.6.11-1.1369_FC4.img
title Windows XP
rootnoverify (hd0,0)
chainloader +1
title GNU Debian Linux 3.1
root (hd1,0)
kernel /boot/vmlinuz-2.6.7-1-386 root=/dev/hda1
initrd /boot/initrd.img-2.6.7-1-386
makeactive
boot
title FreeBSD 5.4 Release
rootnoverify (hd1,2a)
makeactive
chainloader +1

################################################################################
Debian:

title Debian GNU/Linux, kernel 2.6.7-1-386
root (hd0,0)
kernel /boot/vmlinuz-2.6.7-1-386 root=/dev/hda1 ro
initrd /boot/initrd.img-2.6.7-1-386
savedefault
boot

#title Debian GNU/Linux, kernel 2.6.7-1-386 (recovery mode)
#root (hd0,0)
#kernel /boot/vmlinuz-2.6.7-1-386 root=/dev/hda1 ro single
#initrd /boot/initrd.img-2.6.7-1-386
#savedefault
#boot
### END DEBIAN AUTOMAGIC KERNELS LIST

title FreeBSD 5.4release
rootnoverify (hd0,2a)
makeactive
chainloader +1

title Fedora Core 4 (2.6.11-1.1369_FC4)
root (hd1,1)
kernel /boot/vmlinuz-2.6.11-1.1369_FC4 ro root=LABEL=/12 rhgb quiet
initrd /boot/initrd-2.6.11-1.1369_FC4.img

title Windows XP
rootnoverify (hd1,0)
chainloader +1

Any error messages?
Try to edit this section in FC4's config file:See if it works. As for booting Windows, on which drive is it installed? You might need to use Grub's mapping function.