Default Moto G turning off itself

It's a long history.

One day, my Moto G stop charging. He charge until 1%, then turn itself on, and when it was on, it wasn't charging. I thought that was a OS/software problem, but nothing was sloving. I send to warranty and there they send me back saying that a piece was oxidated and was my fault, so they can't help me. When the cellphone arrive back, it was charging normaly. I really doesn't understand. But my PC wasn't showing the smartphone when plugged in the USB port. I started to use AirDroid.

I have a little struggle to update to Android 4.4.2 but I did it. The smartphone was really weird, but I let it go. Now I have the most annoying problem. It keep turning off by itself. I don't know if is software/OS, hardware, some app, something I'm doing wrong, but it's driving me crazy.

Please guys, help =[

P.S.: Sorry my bad english.