highlight the desired kernel which you want to boot ‘fedora core fc9′  press ‘e’ to edit the run levels and other options then the second menu arrives as ..

(hd0,1)

<kernel name> <execution arguments> rhgb quiethighlight the part with quiet and then again press ‘e’

now you will get a prompt to edit the command …

add 1 as

<kernel name> <execution arguments> rhgb quiet 1

space is must…

then press enter

and then press ‘b’ to boot

you will be booted and awarded with a root console….

root@machine#

root@machine#passwd

change the password of root>

Enter New password>

Retype password>

all pasword tokens authenticated….

root@machine#reboot

By editing the grub we edit the kelrnel line from where the OS will get booted. in doing so FC or any other distro it boots the Os kernel with the runlevel one.
In doing so it repairs the the filesystem and reinstalls the users and makes the default value of each password to NULL.
this can be prevented by editing the runlevel from restting the passwd. just add a # to the line of passwd in /boot/boot.conf under the heading of runlevel one.

then you may add the numbers such a 1, 2, 3 to have different run levels.

2 will open in text mode.

suppose you have various kernels on your system then /etc/grub.conf will show

 

title Fedora Core (2.6.12-1.1398_FC4)
root (hd0,0)
kernel /vmlinuz-2.6.12-1.1398_FC8 ro root=LABEL=/1 rhgb quiet
initrd /initrd-2.6.12-1.1398_FC8.img
title Fedora Core (2.6.12-1.1390_FC8)
root (hd0,0)
kernel /vmlinuz-2.6.12-1.1390_FC8 ro root=LABEL=/1 rhgb quiet
initrd /initrd-2.6.12-1.1390_FC8.img
title Fedora Core (2.6.12-1.1387_FC8)
root (hd0,0)
kernel /vmlinuz-2.6.12-1.1387_FC4 ro root=LABEL=/1 rhgb quiet
initrd /initrd-2.6.12-1.1387_FC4.img
title Fedora Core (2.6.11-1.1369_FC8)
root (hd0,0)

you may chnge the preference and remove the hash from password protected grub and edit the password value.