no f8 to start in safe mode.  If your machine hangs at this current time only option is to reinstall.  I am going to setup a couple of machines tomorrow and do more testing.  I am willing to help a few if you have questions, i am no expert but will try.  I thank this blog for introducing me to virtual box.  Never used it before and now i love it.  The system hung up on windows developer preview with the circle going and going and going.