Xen Broke then (Mostly) Fixed

Somehow, Xen has stopped working for me.  My VM's were running.  I used an RDP client to connect to one of the VM's and the Dom-0 froze.  When the Dom-0 came back up, the VM's weren't running like they should be.  I tried starting them.  Xen claimed they started, but I couldn't RDesktop in or ping the VMs.  They would eventually die before the OS came up.  I looked at the Xen logs, and here is what I saw:

Domain 5 has shut down, reason code 1 0x1

dom0 xen # cat xl-dom1.log
Waiting for domain dom1 (domid 1) to die [pid 19733]
Domain 1 has shut down, reason code 1 0x1
Action for shutdown reason code 1 is destroy
Domain 1 needs to be cleaned up: destroying the domain
Done. Exiting now
dom0 xen #

I had no clue what those messages mean.  Xen log messages are really meant for the developers.  For something as complicated as Xen, I don't mind that fact as much.  I tried a few things, like turning off the Dom-0 for a while, then upgrading Xen from 4.2.1 to 4.2.2.  Nothing helped.  Finally, it occurred to me that I had a VNC server listening as well.  Only one of my VMs had the emulated video card outputting to VNC, though.  The other had VGA Passthrough as the primary video card.  I connected to the VM without VGA Passthrough and there was a Windows Startup Recovery screen.  It was asking a question!  I answered the question and told it to reboot.  It rebooted into the Startup Recovery screen again.  Luckily, all this happened the day I performed a backup.  3 minutes to revert one disk and 8 minutes to revert another (I love snapshots!) and I was able to boot.

Unfortunatly, PCI Passthrough had stopped functioning.  The VM with the VGA card was getting a blue screen of death and the VM without it started, but without the USB controller card.