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I'm sorry to hear that but if you think it's hardware related you should get your Local support to inspect the phone, you could repair the phone with PCC but the issue might be motherboard related.
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Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
I'm sorry to hear that, was this phone new or used? if you had issues with the phone since day one, did you contacted the store or Sony?
I'm a bit confused, you bought a brand new Xperia M and you started having issues and instead of contacting your Local support to inspect your device you attempted to repair the phone on your own? thus voiding the warranty, and then you started experiencing more issues?
I wonder if they gave you the same phone, did they sent it in to Sony to get it repaired?