My Apologies for not reading it as VCenter, but as server. However, some things can be confirmed here:
1. the IP you are giving is that of the ESX server, if I am correct?
2. Can you give localhost in the address and try loging using the local machine's credentials where you have installed vCenter.
3. Is it by any chance a part of AD?
4. Have you changed the port number during the vCenter installation? If yes, can you try giving IP:Portnumber and check.
5. Just to make sure can you give the IP of your vCenter in your browser and post the screenshot?