I got problem whit osx instalation, can't erase disc. Macbook turn on but there is apple logo and it turn off and again the same- apple logo- turn off, i can use osx instalation but when i choice whitch osx i want to instal mac turn off. I connect him in external drive mode , i see the disc in disc utility but can't erase it - nothing happening. Cant get to dfu mode too. main board number - 820-01958-A