[Closed] Smartphone won't start - Sony Xperia

It's an xperia arc s.
It rebooted itself randomly when turning the bluetooth on, and now will not fully boot- the sony screen comes up, then xperia screen, then it loops back to the beginning, again and again.... (occasionally gets to the home screen for a fraction of a second).
Cant connect it to the PC companion, although it would connect to the update service (said it was up to date). Running ice cream sandwich. Tried with sim and memory card taken out- no difference.

Any ideas? It's only 4 months old! 🙁