[SOLVED] disastrous curiosity

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http://ubuntuforums.org – hi everyone i pressed ctrl+alt+f1 to log in tty1,then executed Code: lightdm under root privilege for curiosity,then something unexpected took place such as i can't switch back to tty1~6 and the desktop displays abnormally...so how can i recover that thing?i use ubuntu 12.04LTS thanks! (Hardware)