I have been given a broken Macbook Pro that I want to repair to learn more about hardware. The model number on the back is A1226. The unit powers on, but the screen remains black. Is this a motherboard issue or a graphics card issue? If it is a graphics card issue will I have to replace the entire motherboard or is the graphics card seperate? Where can I order either of these (depending on what the issue is). Could the problem be something completely different? Thank you so much for your help!