Hi @frankygmail ,

If you are using the Windows client like below, you should be aware that this is no longer supported. That is why it isn't working. See the below blogpost:

https://blogs.vmware.com/vsphere/2016/05/goodbye-vsphere-client-for-windows-c-hello-html5.html 

Furthermore, you should use the HTML5 client. Just go to the IP address in your browser. From there on you should be able to login to the ESXi host.