So my sister left for college and wouldnt tell us the password to her mac. So i started tinkering with it to try to get into it. I rebooted the mac and found that my keyboard and mouse wouldnt work. Nothing bluetooth or USB related would. The keyboard would only works when i first boot it up and press command s. But when i get to the black screen with white words, i cant type again. So my computer cant do anything now. I have no idea what to do. Please help.