Arduino MEGA 2560 not recognised on OS X

Hi guys, was wondering if you could help me.

I have 2x Arduino MEGA 2560 boards; one being a friend's and one being my own.

Using my own I can connect it to my laptop and it is recognised in the serial port with no problems. When connecting my friend's, however, nothing shows up! Connecting both boards to his laptop both boards will show up and can have sketches uploaded etc, so both boards work fine. Does anyone know the reason I cannot see his on my laptop?

Using OS X EL Capitan 10.11.4 and the 1.6.8 IDE.

Any help would be great!