[Q] how to restart the Sony Ericsson Xperia Arc if frozen

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http://forum.xda-developers.com – my phone is got hanged its not turning on nor turning off it just shows the the sony logo and then it goes on xperia logo but it wont start my phone is not rooted what can be done help me please its version is 4.0.4 .................... Thanks in advance .:crying: (HowTos)