So my sister forgot her Windows 7 password and she was having virus issues anyways so I decided to install Ubuntu 14.04 LTS but it didn't work so I moved her HDD and installed it there and it worked fine but after I moved the HDD back to her PC it always crashes when I log in. I tested it on yet another PC and it worked and when I moved it back to her PC it still crashes at the same spot. Any ideas what's wrong or solutions to fix it please?