Iphone 5s - update/restore problem

Hy,

The iPhone is a Iphone 5S, Space Grey, 16GB, Neverlocked, with iOS 10.2.

A few days ago I've tried to restore my iPhone, using iTunes, because my signal strenght(points) were fluctuating.

Before starting the restore procedure, I did a backup of my Iphone content and saved it on my PC and I have tested the SIM card on my other iPhone and the signal was fine.

During the restore procedure, at one point the iTunes gave me an error, no.50 and stopped the procedure. And my iPhone was blocked in the restore mode.

I have tried all I can find about this problem on your official website, regarding the restore/update procedure. My iTunes is up-to-date, as my PC, that is working on Windows 10, the USB data cable is the one I've received when i bought the iPhone, I've tried with different other original USB cables, in different port, with other computers, even a Mac, and I receive the same error in the middle of the restore process.

Here you have some PrintScreens about what I am trying to explain here.

I have followed all the steps regarding the error 50, but nothing made my iPhone restore.

This is how the iPhone's screen looks when the restore blocks and error 50 pops-up:

Please help!!!!