Hi Abhishek,
Please check the status of your vcenter services using cmd:
service-control --status --all
Try stopping all the vcenter services once and start again:
service-control --stop --all
service-control --start --all
Also, please check the ports are opened and DNS resolves your vcenter FQDN or update host entries.
If you are using proxy, add your vcenter IP/FQDN in the exception list.
Regards, Raj