Check your computer and see if it is installed on your computer. How to do this depends upon your version of Windows. When you find Reader and/or Acrobat let us know the version number and your version of Windows. We can go from there.
On windows, open the Task Manager (Ctrl+Shift+Esc) and check if either Acrobat.exe or AcroRD32.exe is present in the processes list.
If so, then terminate them and try again.