Intermittent problems with VirtualBox, resolved

Trying to upgrade an older Ubuntu VM, I was experiencing intermittent problems during start-up of the VM.  These problems included:

• blank screen
• keyboard/mouse unresponsive

I tried installing Kubuntu to a VM, and also upgrade VirtualBox but continued having the same problems.  Was VirtualBox not compatible with Windows 8.1?  I considered Microsoft's Virtual PC, then tried installing VMWare Player.  Installation of VMWare Player error'd out on the fact that I had Microsoft Hyper-V enabled for Windows Phone development.  

Eventually I realized that Hyper-V might be interfering with VirtualBox.  After disabling Hyper-V, I tried multiple boots of my Linux VMs without encountering the symptoms I had before.