After a scheduled maintenance window, users report that they are unable to access the vCenter...

When users are unable to access the vCenter Server and the vSphere Client is not responding, the first step is to check if the vCenter Server is powered on and whether its essential services are running. This can include services like the vCenter Server service, vSphere Web Client service, and other related services that enable access to the vCenter Server. If the services are stopped or unresponsive, restarting them may resolve the issue.