Install a new instance of VirtualBox on a Windows 7/8/Server 2012 R2. After the install, attempting to start VirtualBox does not show the expected UI. Looking into the Task Manager, shows two VirtualBox processes running.
A thorough search results in a number of help desk discussions around USB support. After unplugging the keyboard and mouse (running the machine “headless” with VNC access) allowed VirtualBox to work. Plugging in a different keyboard and same mouse also worked. So there was something about the original USB keyboard that VirtualBox did not like.
I’ll leave this here and hopefully this can save someone else some time.