Problem:
You can search for vms when you connect to vcenter. What is wrong? Is it your esxi host, your vcenter, your dbs?
You might get
An internal error occurred in the vsphere client. Details: unable to connect to the remote server
Or you might get
Logon to the query service failed.
A connection failure occurred (Unable to connect to the remote server)
Reason:
Check your services
You probably have the Vmware inventory service down on your vcenter.
While you are at it also make sure the serivce Vmware vsphere profile-driven storage is up