Cause problem is there anyway as a conflict of multiple Installations and / or Windows updates. There is a Solution if you dont have snapshop or backup of vm.
Start VM to recovery mode, select commandline. Remove all xcp related drivers with dism.
(use anytoiso to convert xeniface.tar, xenbus.tar, xenvif.tar, xennet.tar, xenvbd.tar and upload iso-Files to xen iso repository)
Load iso as CD/DVD device with contents of drivers tar files and reinstall the drivers manually by dism.
If you are fast, in 5mins Windows is starting as before.