I've manage to install VirtualBox 5.1.2 under Kubuntu 14.04, but not without a major disruption. I retrieved it from the VirtualBox website and followed the defaults to use QApt Package Installer to install it. When I rebooted Kubuntu, the system quit with a blank screen after displaying the initial Kubuntu legend. Bad. bad, bad!
The reason for the disaster was that QApt Package Manager had helpfully removed virtually all of my video supporting software before doing the installation. Fortunately I happened upon a not-so-obvious way to bring my system back to life. I went into recovery mode, then selected Resume. That got me to a login prompt. I logged in, went into superuser mode, and entered the directory where I had stored the virtualbox package. I then did "apt-get -f install vbox...", using autocomplete to select the package. And all my supporting software came back. My system was alive again! This time I used dpkg to install VirtualBox. Rescued!!
The reason for the disaster was that QApt Package Manager had helpfully removed virtually all of my video supporting software before doing the installation. Fortunately I happened upon a not-so-obvious way to bring my system back to life. I went into recovery mode, then selected Resume. That got me to a login prompt. I logged in, went into superuser mode, and entered the directory where I had stored the virtualbox package. I then did "apt-get -f install vbox...", using autocomplete to select the package. And all my supporting software came back. My system was alive again! This time I used dpkg to install VirtualBox. Rescued!!