So.. recently I've been using my computer perfectly until today i opened it and the screen is just flashing with a folder and question mark inside the folder.. i let it flash for some time and it still doesn't go through, so i researched some Google shit and told me to press Command+R to recover.. when i do that.. all i get is a black page with a small Lock in the middle and password field.. and i have no idea what the password is for that since I've never picked that.. any help please?