Ubuntu keeps shuting down by itself (Randomly)

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http://ubuntuforums.org – I've newly installed it, Ubuntu 12.04.03 LTS, and I've installed small programs recently like gnome-schedule, it's a program were I schdule shutdowns, I've added a new task and wrote the command to excute after a specific time which the commad is /sbin/poweroff, so after I deleted the task Ubuntu started shutting down randomly, like after 10 minutes or 1 hour and so on... I've then removed gnome-schdule with the command "apt-get remove gnome-schedule", but the problem keeps persisting. Any way to solve the problem?! (Hardware)