Restart or shutdown the VM
 
Sometime when you try to restart or shutdown the VM, its status get stuck with the yellow status on XenCenter.
To forcely kill that VM:
 Login to the XenServer console where the VM is hosted
 
Get the VM Dom ID 
xe vm-list name-label={VM Name} params=dom-id
 
Get the list of live domains and see if the Domain ID of your VM is listed there
list_domains
 
If your Domain ID VM is there, run the killing script
/opt/xensource/debug/destroy_domain -domid <dom id>
 
Do another list_domain to check the Dom ID is gone
 
Reset the power state of that VM
xe vm-reset-powerstate vm={VM Name} force=true
 
If that still does not work do
xe-toolstack-restar