There is more than a way to skin a cat...

You can stop X by going on a lower run level. Type "sudo init 3" then you will
go on console mode.

To go back to X login to a console and type "sudo init 5" to go in graphic
level.

See : www.debianadmin.com/...buntu-linux-run-levels.html for
details about run levels.

If it doesn't work check error messages in the system log.