So maybe someone has an idea with this! I recently bought this 15" and it was super slow. In my attempt to improve the speed I added more ram and redid the thermal paste as it was getting pretty hot. However, I have never been able to make it successfully boot off anything. It will do a few different things: kernel panic at the Apple, the spinny thing under the apple will just stop, or if I can get it to boot off a Leopard disc you can press the button under the languages and the computer will just freeze up. It did boot up fine prior to taking it apart, but it was super slowwwwww. I've tried two different 1GB ram sticks and it still hates them, I am so lost and just would like to use this thing!!