Just installed Ubuntu 12.4 on my Acer Aspire 5740G laptop, it constantly shuts down itself

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http://askubuntu.com – I don't know what causes it since I just installed Ubuntu on my laptop. Here is the issue. Ubuntu boots normally, so I can use firefox and such. However, after 2-3 minutes, laptop shuts down. (I see Ubuntu logo for 1 second before shutdown.) Fans are usually working loud. GPU drivers (5470) doesn't seem to be installed. Anyone knows what can be the issue? Ps. Previously, I used Windows 7 and it didn't create any issues. (HowTos)