I was given a MacBook Pro 13″ A1278 laptop. While using it, a folder with a blinking question mark came up in the main screen. I could not find a way to get rid of it, so I formatted the HDD and completely erased every thing including the OS, but when I turn on the laptop, the folder and the blinking question mark is still there. I do not know the original OS. How do I fix that blinking icon?