Solved:  I called Dell and paid the $99 to get tech help.  After several attempts to fix the shut down problem it turns out that I should have been using the HDMI port that connects to the upgrade video card port.  The one below the mic and speaker sockets, not the one in the top section..  It seems there is a conflict between the two HDMI ports.  Go figure.  Because this problem first happened during warranty period they were good enough to refund the $99.  Happy day.
When using Zoom my XPS8930 shuts down after about 2 hours.  It comes back on after about 20 minutes.  Last time I heard a short loud fan noise just before shut down.  This has also happened when not in Zoom.  
XPS8930 shuts down and comes back on after 20 minutes