GT2560 failing fw update and bootload burning

[Beppemar]

Hi guys, I'm new in the field of 3d printing, recently I have ordered a prusa i3 pro b and after 2 days building and setting up the machine, this morning as a reward there were two lines of rectangles on the LCD.

I started immediately looking for a solution and I've seen almost all the posts on how to fix this problem, nothing worked until now.

( I'm working over a MacBook Pro with High Sierra, my board is a GT2560 rev A+)

- I've tried to update the firmware but ( either with arduino 1.0.1 or latest build ) the response was a beautiful "avrdude: stk500v2_ReceiveMessage(): timeout"

- At this point I switched over a Windows 7 machine, worse, the Arduino software did not recognise the board through USB. I tried to install a series of drivers but still nothing. ( The led on the board connected to Windows USB lighted up less than normal )

- Then I took my arduino Uno and tried to burn the bootloader but still an error ( either with arduino 1.0.1 or latest build ) : "avrdude: Yikes! Invalid device signature."

I thought there was a easy fix but seems like things are getting more complicated, I really need some help.
Can some component be broken ?
How can I fix It ?
All the help even the stupidest would be appreciated.

Thanks guys.