Kirk, If he VM is not even spinning up then there's some issue with the base mechanics. MInd you, my installs are all vmware on 3.0.X, so I am not sure how much of this applies to Xen and your version, but keep an eye out for the SSVM spinning up. Does it get created and then die off? If not, then the system can't even spin up a basic VM using the system VM iso. If the VM does get spun up long enough to get access to the console, then you can try as I suggested earlier.
However if not even a VM spins up, this is a base mechanics issue with the iso used to spin up system vm's like the console proxy and ssvm and would seem to indicate an issue with the system template used to create the vm's or the inability for the system to use the NFS server to get at the iso template in order to spin up the required VM. hth.
