So wanted to let you know, and maybe someone who has the same problem later on.
I have been to the datacenter and rebooted the ESXi-host. This solved the problems, as it restarted all the services.
I also found the iDRAC Ip adresses of all the hosts in the cluster on the little screen in front of the racks. (And documented it..)
So in the future we will be able to resolve this kind of issues on a remote location.
Henri