My Sony phone died, any ideas why?

I have a Sony Ericsson phone (760w, I think is the model) and it just suddenly died on me for no apparent reason. The battery, which always held a charge for up to a couple days if necessary, was up to almost full charge. I opened it to send a text, the screen did something kind of weird and now the screen is blank and if I leave it on a charger, all it does is make the vibration that it does when I turn the phone on or off. I've had the phone for about 10 or 11 months now. Is it possible that the battery just up and died on me or does it sound like something else is wrong?