Use this command to start headless VirtualBox named NameOfVirtualBox:
Start /b 'C:\Program Files\Oracle\VirtualBox\VBoxHeadless.exe' -s "NameOfVirtualBox"
Or using PowerShell:
Start-Process -FilePath 'C:\Program Files\Oracle\VirtualBox\VBoxHeadless.exe' -ArgumentList @("-s","NameOfVirtualBox") -NoNewWindow
Note: If you close your command prompt the processes with your headless VirtualBox will get killed.
Link to VirtualBox manual : http://www.virtualbox.org/manual/ch07.html#vboxheadless
