Help- New Z710 keeps shutting off

[laurah]

I bought an unlocked Z710i about a month ago for use on Cingular. The phone is great except for the fact that no matter what I do it keeps turning itself off. I've contacted both SE and the third-party vendor and they have both suggested I send the phone to them so that they can look at it though any repairs or replacement would probably not be under warranty (at which point I might as well just buy another phone due to the costs).

Anyone heard or seen a problem like this - spontaneously shutting down of phone? Could it be a software issue? Or a battery issue (though battery is brand new)?

Thanks for any help or suggestions.