XenServer loses its all NIC and settings.
http://support.citrix.com/article/CTX119240
The following are the commands you can try.
host-is-in-emergency-mode
host-is-in-emergency-mode
Returns true if the host the CLI is talking to is currently in emergency mode, false otherwise. This CLI command works directly on slave hosts even with no master host present.
pool-emergency-transition-to-master
pool-emergency-transition-to-master
Instruct a member XenServer host to become the pool master. This command is only accepted by the XenServer host if it has transitioned to emergency mode, meaning it is a member of a pool whose master has disappeared from the network and could not be contacted for some number of retries.XenServer Administrator’s Guide Command line interface 162
Note that this command may cause the password of the host to reset if it has been modified since joining the pool (see the section called “User commands”).
pool-recover-slaves
pool-recover-slaves
Instruct the pool master to try and reset the master address of all members currently running in emergency mode. This is typically used after pool-emergency-transition-to-master has been used to set one of the members as the new master.