There are 3 options to do this, witch way depend on the stuck mode, start with options 1 and work you way thougt it onto the vm is shutdown.
Options 1:
SSH to the Xenserver witch running the vm
Type these commands:
xe task-list
Found the task and the UUID for this task, and kill it
xe task-cancel force=true uuid=<UUID>
Options 2:
SSH to the Xenserver witch running the vm
xe vm-list
Find the vm han get the UUID
list_domains | grep <UUID>
Get the number in front of the UUID
/opt/xensource/debug/destroy_domain -domid <DOMID>
Options 3:
SSH to the Xenserver witch running the vm
xe-toolstack-restart