Burn boot loader to Arduino Mega 2560

I started a Forum a couple of days ago because my Arduinos did´t work. After asking other people and checking the answers on the forum, I think the problem is the boot loader. I´ve tried loading the ArduinoISP code on examples to my Arduino Uno and then I did the appropriate connections to the Mega, set the Uno to Arduino as ISP and then I clicked on Burn Bootloader. But it gave me an error, (I´ll attach the picture of the error).

They have passed me the link to the Nick Gammon tutorial (Gammon Forum : Electronics : Microprocessors : Atmega bootloader programmer) which I did´t understand well, so I don´t know if you can explain me that tutorial.

I´m using a Late 2011 MacBook Pro with Arduino 1.6.0 .

The last two lines in the error dialog box are because I clicked on Serial Monitor after I unplugged the Board to see what had happened.

Thank you.

One thing "Invalid device signature" might mean is that auto-reset has restarted the UNO and your Mac is talking to the Arduino UNO bootloader as if it were the ArduinoISP sketch. The UNO bootloader will give the signature for an ATmega328P when asked and the programmer is expecting the signature for an ATmega2560.

Put a 1 to 10 microfarad capacitor on the UNO between Reset (+) and Ground (-). This will absorb the auto-reset pulse and allow the software to talk to the ArduinoISP sketch.