If you use a virtual machine on Hyper-V Core to manage the Hyper-V operating system, you cannot make changes to the virtual machine that require powering it off because you can’t access the Server Manager
get-vm
and double check that your management VM is not running.get-vm | set-vm -AutomaticStopAction ShutDown
, NOTE: this will change all vm’s that are not currently running to this setting.start-vm nameofwin8vm