If your VirtualCentre server is itself a VM, then it’ll be running on an ESXi host. In the event that the ESXi host is restarted without vMotioning the VirtualCenter Server first (such as when the management network is irrecoveraby unresponsive), then depending on your environment, you may not be able to get a remote connection to the vm after the host has restarted. In this scenario, you’d need to be able to boot the VM from the unsupported console. This is how to do it.
Connect to the iLo or equivalent management interface to the ESX host, send an Alt-F1 and type unsupported followed by the root password to obtain a prompt on the unsupported console.
Identify the VM’s resident on the host
Identify the current power state of the vm running virtual centre
vim-cmd vmsvc/power.getstate ## where ## is the number of the vm identified above
Power on the vm
vim-cmd vmsvc/power.on ## where ## is the number of the vm identified above