Hi,
How long does the phone stay on after power on?
Have you tried turning on the phone without having the SIM card (or memory card, to test) in the phone? We can determine where the issue lies.
Concerning the possibility of software problems, as long as you can get it to stay on, this may resolve it.
If not, a hardware issue is likely, where are you located? You'll have to call local support via these phone numbers: http://www.sonyericsson.com/cws/corporate/common/contact/phonelist
