can not boot in single mode

[Ivan Ferreira]

You should leave it inside.

[Ralph Grothe]

As Alexander already pointed out,
you seem to have a problem with your keyboard
if you cannot type anything at the boot prompt even when booted from a bootable CD.
It is quite common with these PS2 plugs that a pin accidentily gets bent and squeezed.
Check your cabling.

Besides, you don't necessarily need a bootable CD (e.g. installation 1) to get into single user mode.

When the Grub screen appears move with the arrow keys to the boot entry for the kernel you usually auto boot.
When on the line with the vmlinuz* type e to edit the line.
Move to the end of the line and append a space separated s (like single user mode) as kernel argument, and after Esc type b (like boot)
This should bring you to single user mode.
(Note that you have a US keymapping while in Grub, e.g. I always have to type z for y and vice versa because I have a qwertz keyboard)

Also you could append as kernel argument
init=/bin/sh
which should give you a root shell instead of init.
But you have to fsck and remount / rw before you can edit /etc/shadow.

If you don't get the Grub menu displayed it could be that hiddenmenu is set in your grub.conf file.
Just type c to get into Grub command mode.
There help would present you online help of grub commands.
Grub can search for any kernels on your boot devices and has many neat features.
It even can boot via network (if the prerequisites are met).
Read info grub for details.