Hello, I'm new to this, I bought a used MacBook from a lady but she did not know her password for the computer, so I went online and saw that if hold down command and r keys while booting the computer up it will bring you to the OS X utilities options, then it said to go into the disk utility then highlight the Macintosh HD then erase it. once I did that it said to go back and clink on reinstall OS X, once I clicked that and hit continue a error comes up and is say to try and run the application again. so that didn't work so I tried holding down the command and S while start up to reset the computer that was but the ROOT does not show up it comes up with -sh-3.2# not sure what to do now lol, maybe some one can help me thanks!