I have a 2015 model Mac book pro i5 and I am having issues with it booting up.... I got the Mac from my brother who upgraded to the 2017 mbp... his hdd died and he gave me a new.one... the issues in having is the screen pops up with a grey blinking folder with a question mark... I've tried holding c... ive.tried holding option + r... and when I do that it takes me to a screen with a pad lock and a spot to enter a password... when I click the box it doesn't allow me to enter anything... I bought a new osx snow leopard to try to do.a fresh I stall of osx... since I can't get Into any boot menu... it's useless... any ideas for a bypass to all this??