After installing the latest Windows updates and restarting the server you get the message ‘Preparing to configure Windows – Do not turn off your computer’ which seems like it has hung.
Initially I was unable to connect to the server at all via vSphere client or RDP. After a mild panic I connected to each vSphere node with the vSphere client until I found the server that was hosting the vCentre server. I was then able to access the console.
Panic over I decided to restart the server which kick started whatever update had crashed the server and I was able to then log in.