phone refuses to start after entering correct code , keeps cycling thru power up screens,

[Uliwooly]

Could you elaborate?

[a17ggt]

Turned phone off last night, had no problems, went to turn it on, entered pin code, the phone does its start up cycle, the last screen freezes, goes black then asks for my again, back to square 1, have tried turning phone off on the back off swirch

[Uliwooly]

repair your phone 

Update Service (SUS)

PC Companion (PCC)

Bridge (for Mac)

Alternatives on How to backup Xperias

http://talk.sonymobile.com/thread/36355