. i had to restart server. any idea?
It means that the hostd agent agent on your server was not granted enough resources to update its status. This could be the server is under stress and no free cpu cycles are available.
while start vSphere Client, when i access to vSphere window
Check if any other process is hogging the memory by esxtop.
And of course, are you using the vsphere client matching the ESXi server version 