I try to access the boot menu, where you can choose a kernel and,
whatever key I press, I can't stop the countdown and access the boot
menu.
I checked /boot/grub/grub.conf and I have hiddenmenu in it. But the
back-up, /boot/grub/grub.conf~ dates back to August and has hiddenmenu
in it too. Since I accessed the boot menu since August, I suppose this
is not the problem.