Does your system start? Or not? If it starts, use your Security Programs to get rid of it, or Malwarebytes, http://www.malwarebytes.org/. That would be the safest way.
Or you can go to Windows Safe Mode - press F8 when you start your computer, and keep it down 'til something happens - and, from there you can find it in Explorer and unharm the dll. I suggest you move it to a desktop folder, or make it a zip file; that way you have an option to return it, in case something went wrong. BUT you have to get it out from where it is now.