Having been through these steps numerous times under the guidance of Mac Applecare techs with a seven month-old 15" Macbook Pro running Snow Leopard (10.6.8) and re-installing the OS twice all I can say is that I've got a 'LEMON'! The claimed reliability of Apple Mac and its software in no way resembles my experience to date. I've posted a thread to this effect in the hope someone out there has a solution