Xperia S stuck in a loop

[GM852]

Hello! i got a problem with an Xperia S. I got it from my sister, she said that something was wrong with the phone, it wasn't charging!

So i was taking a look and something strange is happening with the phone:

First: It never finish charging! it's always at a red led but it never goes green.

Second: Sometimes after leaving the phone at the charger, the led goes off and the phone goes to the Sony boot screen, but after some seconds, the phone suddenly goes off and the red led goes on again.

Thirdy: I can get the phone on fastboot mode, but i can't flash a new system for example. Everytime a try to flash a new system, the phone goes off in the middle of the process and the red led again goes on.

Can anyone help me?