Forgot to mention that when this happens his computer is still running fine, its just the monitor that comes up with the graphical error.
For example, i was talking to him on skype and the graphical error occurred and i was still able to talk to him on skype.
To me that kinda confirms that it is a graphical error.
Is there any chance that it could be caused by the monitor itself being faulty. I personally don't think so but I'm not an expert on graphical errors obviously :S